SEES-hacks: SEESenv/web/html/ch2intro.html@10074d1357ff (annotated)

0 8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	1	<html>
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	2	<head>
6 1ce9b33fb6ff sorted the problem related to paths amit@thunder parents: 2 diff changeset	3	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
1ce9b33fb6ff sorted the problem related to paths amit@thunder parents: 2 diff changeset	4	<title>
1ce9b33fb6ff sorted the problem related to paths amit@thunder parents: 2 diff changeset	5	Chapter. intro
1ce9b33fb6ff sorted the problem related to paths amit@thunder parents: 2 diff changeset	6	</title>
15 f2383fee6584 Testing amit@thunder parents: 6 diff changeset	7	<link rel="stylesheet" href="/review/support/styles.css" type="text/css" />
f2383fee6584 Testing amit@thunder parents: 6 diff changeset	8	<meta name="generator" content="DocBook XSL Stylesheets V1.74.3" />
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f2383fee6584 Testing amit@thunder parents: 6 diff changeset	11	</script>
f2383fee6584 Testing amit@thunder parents: 6 diff changeset	12	<script type="text/javascript" src="/review/support/form.js">
f2383fee6584 Testing amit@thunder parents: 6 diff changeset	13	</script>
f2383fee6584 Testing amit@thunder parents: 6 diff changeset	14	<script type="text/javascript" src="/review/support/hsbook.js">
f2383fee6584 Testing amit@thunder parents: 6 diff changeset	15	</script>
6 1ce9b33fb6ff sorted the problem related to paths amit@thunder parents: 2 diff changeset	16	</head>
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	17	<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" title="Chapter 1. ">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	18	<div class="titlepage"></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	19	<div class="toc">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	20	<p><b>Table of Contents</b></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	21	<dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	22	<dt><span class="article"><a href="#id2580245">Basic Python</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	23	<dd><dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	24	<dt><span class="section"><a href="#id2388008">1. Introduction</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	25	<dt><span class="section"><a href="#id2631374">2. The Python Interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	26	<dd><dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	27	<dt><span class="section"><a href="#id2631383">2.1. The Interactive Interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	28	<dt><span class="section"><a href="#id2631556">2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	29	</dl></dd>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	30	<dt><span class="section"><a href="#id2631681">3. Editing and running a python file</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	31	<dt><span class="section"><a href="#id2631788">4. Basic Datatypes and operators in Python</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	32	<dd><dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	33	<dt><span class="section"><a href="#id2631822">4.1. Numbers</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	34	<dt><span class="section"><a href="#id2631952">4.2. Variables</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	35	<dt><span class="section"><a href="#id2632000">4.3. Strings</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	36	<dt><span class="section"><a href="#id2632194">4.4. Boolean</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	37	</dl></dd>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	38	<dt><span class="section"><a href="#id2632223">5. The <span class="strong"><strong>while</strong></span> loop</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	39	<dt><span class="section"><a href="#id2632260">6. The <span class="strong"><strong>if</strong></span> conditional</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	40	<dt><span class="section"><a href="#id2632330">7. <span class="strong"><strong>raw_input()</strong></span></a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	41	<dt><span class="section"><a href="#id2632484">8. <span class="strong"><strong>int()</strong></span> method</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	42	</dl></dd>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	43	</dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	44	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	45	<div class="article" title="Basic Python">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	46	<div class="titlepage">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	47	<div><div><h2 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	48	<a name="id2580245"></a>Basic Python</h2></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	49	<hr>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	50	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	51	<div class="toc">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	52	<p><b>Table of Contents</b></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	53	<dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	54	<dt><span class="section"><a href="#id2388008">1. Introduction</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	55	<dt><span class="section"><a href="#id2631374">2. The Python Interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	56	<dd><dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	57	<dt><span class="section"><a href="#id2631383">2.1. The Interactive Interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	58	<dt><span class="section"><a href="#id2631556">2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	59	</dl></dd>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	60	<dt><span class="section"><a href="#id2631681">3. Editing and running a python file</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	61	<dt><span class="section"><a href="#id2631788">4. Basic Datatypes and operators in Python</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	62	<dd><dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	63	<dt><span class="section"><a href="#id2631822">4.1. Numbers</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	64	<dt><span class="section"><a href="#id2631952">4.2. Variables</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	65	<dt><span class="section"><a href="#id2632000">4.3. Strings</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	66	<dt><span class="section"><a href="#id2632194">4.4. Boolean</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	67	</dl></dd>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	68	<dt><span class="section"><a href="#id2632223">5. The <span class="strong"><strong>while</strong></span> loop</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	69	<dt><span class="section"><a href="#id2632260">6. The <span class="strong"><strong>if</strong></span> conditional</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	70	<dt><span class="section"><a href="#id2632330">7. <span class="strong"><strong>raw_input()</strong></span></a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	71	<dt><span class="section"><a href="#id2632484">8. <span class="strong"><strong>int()</strong></span> method</a></span></dt>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	72	</dl>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	73	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	74	<p><a name="ch2intro_1"></a>This document is intended to be handed out at the end of the workshop. It has
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	75	been designed for Engineering students who are Python beginners and have basic
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	76	programming skills. The focus is on basic numerics and plotting using Python.</p>The system requirements:<div class="itemizedlist"><ul class="itemizedlist" type="*">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	77	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_2"></a>Python - version 2.5.x or newer.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	78	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_3"></a>IPython</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	79	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_4"></a>Text editor - scite, vim, emacs or whatever you are comfortable with.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	80	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	81	<div class="section" title="1. Introduction">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	82	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	83	<a name="id2388008"></a>1. Introduction</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	84	<p><a name="ch2intro_5"></a>The Python programming language was created by a dutch named Guido van Rossum.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	85	The idea of Python was conceived in December 1989. The name Python has nothing
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	86	to do with the reptilian, but its been named after the 70s comedy series
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	87	"Monty Python's Flying Circus", since it happens to be Guido's favourite
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	88	TV series.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	89	<p><a name="ch2intro_6"></a>Current stable version of Python is 2.6.x, although Python 3.0 is also the stable
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	90	version, it is not backwards compatible with the previous versions and is hence
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	91	not entirely popular at the moment. This material will focus on the 2.6.x series.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	92	<p><a name="ch2intro_7"></a>Python is licensed under the Python Software Foundation License (PSF License)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	93	which is GPL compatible Free Software license (excepting license version 1.6 and 2.0)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	94	It is a no strings attached license, which means the source code is free to modify
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	95	and redistribute.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	96	<p><a name="ch2intro_8"></a>The Python docs define Python as "Python is an interpreted, object-oriented,
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	97	high-level programming language with dynamic semantics." A more detailed summary
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	98	can be found at </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	99	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	100	<div class="titlepage"><hr></div>http://www.python.org/doc/essays/blurb.html</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	101	<p>. Python is a language that
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	102	has been designed to help the programmer concentrate on solving the problem at hand
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	103	and not worry about the programming language idiosyncrasies.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	104	<p><a name="ch2intro_9"></a>Python is a highly cross platform compatible language on account of it being an
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	105	interpreted language. It is highly scalable and hence has been adapted to run on
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	106	the Nokia 60 series phones. Python has been designed to be readable and easy to use</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	107	<p><a name="ch2intro_a"></a><span class="strong"><strong>Resources available for reference</strong></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	108	<div class="itemizedlist"><ul class="itemizedlist" type="*">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	109	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	110	<p><a name="ch2intro_b"></a>Web: </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	111	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	112	<div class="titlepage"><hr></div>http://www.python.org</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	113	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	114	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	115	<p><a name="ch2intro_c"></a>Doc: </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	116	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	117	<div class="titlepage"><hr></div>http://www.python.org/doc</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	118	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	119	<li class="listitem" style="list-style-type: ">Free Tutorials:<div class="itemizedlist"><ul class="itemizedlist" type="">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	120	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	121	<p><a name="ch2intro_d"></a>Official Python Tutorial: </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	122	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	123	<div class="titlepage"><hr></div>http://docs.python.org/tut/tut.html</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	124	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	125	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	126	<p><a name="ch2intro_e"></a>Byte of Python: </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	127	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	128	<div class="titlepage"><hr></div>http://www.byteofpython.info/</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	129	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	130	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	131	<p><a name="ch2intro_f"></a>Dive into Python: </p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	132	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	133	<div class="titlepage"><hr></div>http://diveintopython.org/</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	134	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	135	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	136	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	137	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	138	<p><a name="ch2intro_10"></a><span class="strong"><strong>Advantages of Python - Why Python??</strong></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	139	<div class="itemizedlist"><ul class="itemizedlist" type="*">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	140	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_11"></a>Python has been designed for readability and ease of use. Its been designed in
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	141	such a fashion that it imposes readability on the programmer. Python does away
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	142	with the braces and the semicolons and instead implements code blocks based on
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	143	indentation, thus enhancing readability.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	144	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_12"></a>Python is a high level, interpreted, modular and object oriented language.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	145	Python performs memory management on its own, thus the programmer need not bother
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	146	about allocating and deallocating memory to variables. Python provides extensibility
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	147	by providing modules which can be easily imported similar to headers in C and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	148	packages in Java. Python is object oriented and hence provides all the object oriented
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	149	characteristics such as inheritance, encapsulation and polymorphism.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	150	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_13"></a>Python offers a highly powerful interactive programming interface in the form
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	151	of the 'Interactive Interpreter' which will be discussed in more detail in the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	152	following sections.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	153	<li class="listitem" style="list-style-type: *">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	154	<p><a name="ch2intro_14"></a>Python provides a rich standard library and an extensive set of modules. The
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	155	power of Python modules can be seen in this slightly exaggerated cartoon
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	156	</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	157	<div class="reference">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	158	<div class="titlepage"><hr></div>http://xkcd.com/353/</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	159	</li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	160	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_15"></a>Python interfaces well with most other programming languages such as C, C++
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	161	and FORTRAN.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	162	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	163	<p><a name="ch2intro_16"></a>Although, Python has one setback. Python is not fast as some of the compiled
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	164	languages like C or C++. Yet, the amount of flexibility and power more than make
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	165	up for this setback.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	166	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	167	<div class="section" title="2. The Python Interpreter">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	168	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	169	<a name="id2631374"></a>2. The Python Interpreter</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	170	<div class="section" title="2.1. The Interactive Interpreter">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	171	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	172	<a name="id2631383"></a>2.1. The Interactive Interpreter</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	173	<p><a name="ch2intro_17"></a>Typing <span class="emphasis"><em>python</em></span> at the shell prompt on any standard Unix/Gnu-Linux system and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	174	hitting the enter key fires up the Python 'Interactive Interpreter'. The Python
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	175	interpreter is one of the most integral features of Python. The prompt obtained
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	176	when the interactive interpreter is similar to what is shown below. The exact
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	177	appearance might differ based on the version of Python being used. The <code class="literal">>>></code>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	178	thing shown is the python prompt. When something is typed at the prompt and the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	179	enter key is hit, the python interpreter interprets the command entered and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	180	performs the appropriate action. All the examples presented in this document are
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	181	to be tried hands on, on the interactive interpreter.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	182	<pre class="programlisting">Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	183	[GCC 4.3.2] on linux2
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	184	Type "help", "copyright", "credits" or "license" for more information.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	185	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	186	<p><a name="ch2intro_18"></a>Lets try with an example, type <code class="literal">print 'Hello, World!'</code> at the prompt and hit
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	187	the enter key.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	188	<pre class="programlisting">>>> print 'Hello, World!'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	189	Hello, World!</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	190	<p><a name="ch2intro_19"></a>This example was quite straight forward, and thus we have written our first
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	191	line of Python code. Now let us try typing something arbitrary at the prompt.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	192	For example:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	193	<pre class="programlisting">>>> arbit word
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	194	File "<stdin>", line 1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	195	arbit word
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	196	^
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	197	SyntaxError: invalid syntax
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	198	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	199	<p><a name="ch2intro_1a"></a>The interpreter gave an error message saying that 'arbit word' was invalid
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	200	syntax which is valid. The interpreter is an amazing tool when learning to
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	201	program in Python. The interpreter provides a help function that provides the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	202	necessary documentation regarding all Python syntax, constructs, modules and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	203	objects. Typing <span class="emphasis"><em>help()</em></span> at the prompt gives the following output:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	204	<pre class="programlisting">>>> help()
0 8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	205
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	206	Welcome to Python 2.5! This is the online help utility.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	207
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	208	If this is your first time using Python, you should definitely check out
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	209	the tutorial on the Internet at http://www.python.org/doc/tut/.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	210
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	211	Enter the name of any module, keyword, or topic to get help on writing
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	212	Python programs and using Python modules. To quit this help utility and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	213	return to the interpreter, just type "quit".
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	214
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	215	To get a list of available modules, keywords, or topics, type "modules",
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	216	"keywords", or "topics". Each module also comes with a one-line summary
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	217	of what it does; to list the modules whose summaries contain a given word
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	218	such as "spam", type "modules spam".
1 672eaaab9204 Added some new html files that failed earlier during change from rst amit@thunder parents: 0 diff changeset	219
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	220	help></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	221	<p><a name="ch2intro_1b"></a>As mentioned in the output, entering the name of any module, keyword or topic
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	222	will provide the documentation and help regarding the same through the online
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	223	help utility. Pressing <span class="emphasis"><em>Ctrl+d</em></span> exits the help prompt and returns to the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	224	python prompt.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	225	<p><a name="ch2intro_1c"></a>Let us now try a few examples at the python interpreter.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	226	<p><a name="ch2intro_1d"></a>Eg 1:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	227	<pre class="programlisting">>>> print 'Hello, python!'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	228	Hello, python!
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	229	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	230	<p><a name="ch2intro_1e"></a>Eg 2:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	231	<pre class="programlisting">>>> print 4321*567890
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	232	2453852690
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	233	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	234	<p><a name="ch2intro_1f"></a>Eg 3:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	235	<pre class="programlisting">>>> 4321*567890
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	236	2453852690L
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	237	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	238	<pre class="programlisting">Note: Notice the 'L' at the end of the output. The 'L' signifies that the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	239	output of the operation is of type long. It was absent in the previous
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	240	example because we used the print statement. This is because print formats
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	241	the output before displaying.</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	242	<p><a name="ch2intro_20"></a>Eg 4:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	243	<pre class="programlisting">>>> big = 12345678901234567890 ** 3
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	244	>>> print big
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	245	1881676372353657772490265749424677022198701224860897069000
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	246	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	247	<pre class="programlisting">This example is to show that unlike in C or C++ there is no limit on the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	248	value of an integer.</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	249	<p><a name="ch2intro_21"></a>Try this on the interactive interpreter:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	250	<code class="literal">import this</code></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	251	<p><a name="ch2intro_22"></a><span class="emphasis"><em>Hint: The output gives an idea of Power of Python</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	252	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	253	<div class="section" title="2.2. ipython - An enhanced interactive Python interpreter">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	254	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	255	<a name="id2631556"></a>2.2. <span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	256	<p><a name="ch2intro_23"></a>The power and the importance of the interactive interpreter was the highlight
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	257	of the previous section. This section provides insight into the enhanced
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	258	interpreter with more advanced set of features called <span class="strong"><strong>ipython</strong></span>. Entering
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	259	<span class="emphasis"><em>ipython</em></span> at the shell prompt fires up the interactive interpreter.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	260	<pre class="programlisting">$ ipython
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	261	Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	262	Type "copyright", "credits" or "license" for more information.
1 672eaaab9204 Added some new html files that failed earlier during change from rst amit@thunder parents: 0 diff changeset	263
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	264	IPython 0.8.4 -- An enhanced Interactive Python.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	265	? -> Introduction and overview of IPython's features.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	266	%quickref -> Quick reference.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	267	help -> Python's own help system.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	268	object? -> Details about 'object'. ?object also works, ?? prints more.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	269
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	270	In [1]:</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	271	<p><a name="ch2intro_24"></a>This is the output obtained upon firing ipython. The exact appearance may
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	272	change based on the Python version installed. The following are some of the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	273	various features provided by <span class="strong"><strong>ipython</strong></span>:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	274	<p><a name="ch2intro_25"></a>Suggestions - ipython provides suggestions of the possible methods and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	275	operations available for the given python object.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	276	<p><a name="ch2intro_26"></a>Eg 5:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	277	<pre class="programlisting">In [4]: a = 6
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	278
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	279	In [5]: a.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	280	a.__abs__ a.__divmod__ a.__index__ a.__neg__ a.__rand__ a.__rmod__ a.__rxor__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	281	a.__add__ a.__doc__ a.__init__ a.__new__ a.__rdiv__ a.__rmul__ a.__setattr__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	282	a.__and__ a.__float__ a.__int__ a.__nonzero__ a.__rdivmod__ a.__ror__ a.__str__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	283	a.__class__ a.__floordiv__ a.__invert__ a.__oct__ a.__reduce__ a.__rpow__ a.__sub__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	284	a.__cmp__ a.__getattribute__ a.__long__ a.__or__ a.__reduce_ex__ a.__rrshift__ a.__truediv__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	285	a.__coerce__ a.__getnewargs__ a.__lshift__ a.__pos__ a.__repr__ a.__rshift__ a.__xor__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	286	a.__delattr__ a.__hash__ a.__mod__ a.__pow__ a.__rfloordiv__ a.__rsub__
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	287	a.__div__ a.__hex__ a.__mul__ a.__radd__ a.__rlshift__ a.__rtruediv__</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	288	<p><a name="ch2intro_27"></a>In this example, we initialized 'a' (a variable - a concept that will be
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	289	discussed in the subsequent sections.) to 6. In the next line when the <span class="emphasis"><em>tab</em></span> key
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	290	is pressed after typing '<span class="emphasis"><em>a.</em></span>' ipython displays the set of all possible methods
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	291	that are applicable on the object 'a' (an integer in this context). Ipython
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	292	provides many such datatype specific features which will be presented in the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	293	further sections as and when the datatypes are introduced.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	294	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	295	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	296	<div class="section" title="3. Editing and running a python file">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	297	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	298	<a name="id2631681"></a>3. Editing and running a python file</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	299	<p><a name="ch2intro_28"></a>The previous sections focused on the use of the interpreter to run python code.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	300	While the interpeter is an excellent tool to test simple solutions and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	301	experiment with small code snippets, its main disadvantage is that everything
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	302	written in the interpreter is lost once its quit. Most of the times a program is
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	303	used by people other than the author. So the programs have to be available in
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	304	some form suitable for distribution, and hence they are written in files. This
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	305	section will focus on editing and running python files. Start by opening a text
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	306	editor ( it is recommended you choose one from the list at the top of this page ).
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	307	In the editor type down python code and save the file with an extension <span class="strong"><strong>.py</strong></span>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	308	(python files have an extension of .py). Once done with the editing, save the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	309	file and exit the editor.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	310	<p><a name="ch2intro_29"></a>Let us look at a simple example of calculating the gcd of 2 numbers using Python:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	311	<p><a name="ch2intro_2a"></a><span class="strong"><strong>Creating the first python script(file)</strong></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	312	<pre class="programlisting">$ emacs gcd.py
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	313	def gcd(x,y):
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	314	if x % y == 0:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	315	return y
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	316	return gcd(y, x%y)
1 672eaaab9204 Added some new html files that failed earlier during change from rst amit@thunder parents: 0 diff changeset	317
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	318	print gcd(72, 92)</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	319	<p><a name="ch2intro_2b"></a>To run the script, open the shell prompt, navigate to the directory that
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	320	contains the python file and run <code class="literal">python <filename.py></code> at the prompt ( in this
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	321	case filename is gcd.py )</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	322	<p><a name="ch2intro_2c"></a><span class="strong"><strong>Running the python script</strong></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	323	<pre class="programlisting">$ python gcd.py
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	324	4
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	325	$</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	326	<p><a name="ch2intro_2d"></a>Another method to run a python script would be to include the line</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	327	<p><a name="ch2intro_2e"></a><code class="literal">#! /usr/bin/python</code></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	328	<p><a name="ch2intro_2f"></a>at the beginning of the python file and then make the file executable by</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	329	<p><a name="ch2intro_30"></a>$ chmod a+x <span class="emphasis"><em>filename.py</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	330	<p><a name="ch2intro_31"></a>Once this is done, the script can be run as a standalone program as follows:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	331	<p><a name="ch2intro_32"></a>$ ./<span class="emphasis"><em>filename.py</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	332	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	333	<div class="section" title="4. Basic Datatypes and operators in Python">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	334	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	335	<a name="id2631788"></a>4. Basic Datatypes and operators in Python</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	336	<p><a name="ch2intro_33"></a>Python provides the following set of basic datatypes.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	337	<div class="itemizedlist"><ul class="itemizedlist" type="*">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	338	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_34"></a>Numbers: int, float, long, complex</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	339	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_35"></a>Strings</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	340	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_36"></a>Boolean</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	341	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	342	<div class="section" title="4.1. Numbers">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	343	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	344	<a name="id2631822"></a>4.1. Numbers</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	345	<p><a name="ch2intro_37"></a>Numbers were introduced in the examples presented in the interactive interpreter
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	346	section. Numbers include types as mentioned earlier viz., int (integers), float
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	347	(floating point numbers), long (large integers), complex (complex numbers with
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	348	real and imaginary parts). Python is not a strongly typed language, which means
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	349	the type of a variable need not mentioned during its initialization. Let us look
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	350	at a few examples.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	351	<p><a name="ch2intro_38"></a>Eg 6:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	352	<pre class="programlisting">>>> a = 1 #here a is an integer variable</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	353	<p><a name="ch2intro_39"></a>Eg 7:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	354	<pre class="programlisting">>>> lng = 122333444455555666666777777788888888999999999 #here lng is a variable of type long
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	355	>>> lng
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	356	122333444455555666666777777788888888999999999L #notice the trailing 'L'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	357	>>> print lng
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	358	122333444455555666666777777788888888999999999 #notice the absence of the trailing 'L'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	359	>>> lng+1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	360	122333444455555666666777777788888889000000000L</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	361	<p><a name="ch2intro_3a"></a>Long numbers are the same as integers in almost all aspects. They can be used in
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	362	operations just like integers and along with integers without any distinction.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	363	The only distinction comes during type checking (which is not a healthy practice).
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	364	Long numbers are tucked with a trailing 'L' just to signify that they are long.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	365	Notice that in the example just lng at the prompt displays the value of the variable
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	366	with the 'L' whereas <code class="literal">print lng</code> displays without the 'L'. This is because print
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	367	formats the output before printing. Also in the example, notice that adding an
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	368	integer to a long does not give any errors and the result is as expected. So for
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	369	all practical purposes longs can be treated as ints.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	370	<p><a name="ch2intro_3b"></a>Eg 8:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	371	<pre class="programlisting">>>> fl = 3.14159 #fl is a float variable
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	372	>>> e = 1.234e-4 #e is also a float variable, specified in the exponential form
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	373	>>> a = 1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	374	>>> b = 2
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	375	>>> a/b #integer division
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	376	0
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	377	>>> a/fl #floating point division
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	378	0.31831015504887655
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	379	>>> e/fl
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	380	3.9279473133031364e-05</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	381	<p><a name="ch2intro_3c"></a>Floating point numbers, simply called floats are real numbers with a decimal point.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	382	The example above shows the initialization of a float variable. Shown also in this
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	383	example is the difference between integer division and floating point division.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	384	'a' and 'b' here are integer variables and hence the division gives 0 as the quotient.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	385	When either of the operands is a float, the operation is a floating point division,
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	386	and the result is also a float as illustrated.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	387	<p><a name="ch2intro_3d"></a>Eg 9:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	388	<pre class="programlisting">>>> cplx = 3 + 4j #cplx is a complex variable
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	389	>>> cplx
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	390	(3+4j)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	391	>>> print cplx.real #prints the real part of the complex number
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	392	3.0
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	393	>>> print cplx.imag #prints the imaginary part of the complex number
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	394	4.0
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	395	>>> print cplx*fl #multiplies the real and imag parts of the complex number with the multiplier
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	396	(9.42477+12.56636j)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	397	>>> abs(cplx) #returns the absolute value of the complex number
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	398	5.0</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	399	<p><a name="ch2intro_3e"></a>Python provides a datatype for complex numbers. Complex numbers are initialized
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	400	as shown in the example above. The <span class="emphasis"><em>real</em></span> and <span class="emphasis"><em>imag</em></span> operators return the real and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	401	imaginary parts of the complex number as shown. The <span class="emphasis"><em>abs()</em></span> returns the absolute
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	402	value of the complex number.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	403	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	404	<div class="section" title="4.2. Variables">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	405	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	406	<a name="id2631952"></a>4.2. Variables</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	407	<p><a name="ch2intro_3f"></a>Variables are just names that represent a value. Variables have already been
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	408	introduced in the various examples from the previous sections. Certain rules about
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	409	using variables:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	410	<div class="itemizedlist"><ul class="itemizedlist" type="*">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	411	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_40"></a>Variables have to be initialized or assigned a value before being used.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	412	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_41"></a>Variable names can consist of letters, digits and underscores(_).</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	413	<li class="listitem" style="list-style-type: *"><p><a name="ch2intro_42"></a>Variable names cannot begin with digits, but can contain digits in them.</p></li>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	414	</ul></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	415	<p><a name="ch2intro_43"></a>In reference to the previous section examples, 'a', 'b', 'lng', 'fl', 'e' and 'cplx'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	416	are all variables of various datatypes.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	417	<pre class="programlisting">Note: Python is not a strongly typed language and hence an integer variable can at a
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	418	later stage be used as a float variable as well.</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	419	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	420	<div class="section" title="4.3. Strings">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	421	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	422	<a name="id2632000"></a>4.3. Strings</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	423	<p><a name="ch2intro_44"></a>Strings are one of the essential data structures of any programming language.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	424	The <code class="literal">print "Hello, World!"</code> program was introduced in the earlier section, and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	425	the <span class="emphasis"><em>"Hello, World!"</em></span> in the print statement is a string. A string is basically
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	426	a set of characters. Strings can be represented in various ways shown below:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	427	<pre class="programlisting">s = 'this is a string' # a string variable can be represented using single quotes
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	428	s = 'This one has "quotes" inside!' # The string can have quotes inside it as shown
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	429	s = "I have 'single-quotes' inside!"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	430	l = "A string spanning many lines\
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	431	one more line\
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	432	yet another" # a string can span more than a single line.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	433	t = """A triple quoted string does # another way of representing multiline strings.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	434	not need to be escaped at the end and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	435	"can have nested quotes" etc."""</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	436	<p><a name="ch2intro_45"></a>Try the following on the interpreter:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	437	<code class="literal">s = 'this is a string with 'quotes' of similar kind'</code></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	438	<p><a name="ch2intro_46"></a><span class="strong"><strong>Exercise: How to use single quotes within single quotes in a string as shown
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	439	in the above example without getting an error?</strong></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	440	<div class="section" title="4.3.1. String operations">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	441	<div class="titlepage"><div><div><h4 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	442	<a name="id2632051"></a>4.3.1. String operations</h4></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	443	<p><a name="ch2intro_47"></a>A few basic string operations are presented here.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	444	<p><a name="ch2intro_48"></a><span class="strong"><strong>String concatenation</strong></span>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	445	String concatenation is done by simple addition of two strings.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	446	<pre class="programlisting">>>> x = 'Hello'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	447	>>> y = ' Python'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	448	>>> print x+y
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	449	Hello Python</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	450	<p><a name="ch2intro_49"></a><span class="emphasis"><em>Try this yourself:</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	451	<pre class="programlisting">>>> somenum = 13
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	452	>>> print x+somenum</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	453	<p><a name="ch2intro_4a"></a>The problem with the above example is that here a string variable and an integer
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	454	variable are trying to be concantenated. To obtain the desired result from the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	455	above example the str(), repr() and the `` can be used.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	456	<p><a name="ch2intro_4b"></a><span class="strong"><strong>str()</strong></span> simply converts a value to a string in a reasonable form.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	457	<span class="strong"><strong>repr()</strong></span> creates a string that is a representation of the value.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	458	<p><a name="ch2intro_4c"></a>The difference can be seen in the example shown below:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	459	<pre class="programlisting">>>> str(1000000000000000000000000000000000000000000000000L)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	460	'1000000000000000000000000000000000000000000000000'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	461	>>> repr(1000000000000000000000000000000000000000000000000L)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	462	'1000000000000000000000000000000000000000000000000L'</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	463	<p><a name="ch2intro_4d"></a>It can be observed that the 'L' in the long value shown was omitted by str(),
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	464	whereas repr() converted that into a string too. An alternative way of using
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	465	repr(value) is <code class="literal">`value`</code>.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	466	<p><a name="ch2intro_4e"></a>A few more examples:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	467	<pre class="programlisting">>>> x = "Let's go \nto Pycon"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	468	>>> print x
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	469	Let's go
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	470	to Pycon</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	471	<p><a name="ch2intro_4f"></a>In the above example, notice that the 'n'(newline) character is formatted and
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	472	the string is printed on two lines. The strings discussed until now were normal
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	473	strings. Other than these there are two other types of strings namely, raw strings
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	474	and unicode strings.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	475	<p><a name="ch2intro_50"></a><span class="strong"><strong>Raw strings</strong></span> are strings which are unformatted, that is the backslashes() are
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	476	not parsed and are left as it is in the string. Raw strings are represented with
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	477	an 'r' at the start of a string.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	478	Let us look at an example</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	479	<pre class="programlisting">>>> x = r"Let's go \nto Pycon"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	480	>>> print x
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	481	Let's go \nto Pycon</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	482	<p><a name="ch2intro_51"></a>Note: The 'n' is not being parsed into a new line and is left as it is.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	483	<p><a name="ch2intro_52"></a><span class="emphasis"><em>Try this yourself:</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	484	<pre class="programlisting">>>> x = r"Let's go to Pycon\"</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	485	<p><a name="ch2intro_53"></a><span class="strong"><strong>Unicode strings</strong></span> are strings where the characters are Unicode characters as
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	486	opposed to ASCII characters. Unicode strings are represented with a 'u' at the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	487	start of the string.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	488	Let us look at an example:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	489	<pre class="programlisting">>>> x = u"Let's go to Pycon!"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	490	>>> print x
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	491	Let's go to Pycon!</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	492	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	493	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	494	<div class="section" title="4.4. Boolean">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	495	<div class="titlepage"><div><div><h3 class="title">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	496	<a name="id2632194"></a>4.4. Boolean</h3></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	497	<p><a name="ch2intro_54"></a>Python also provides special Boolean datatype. A boolean variable can assume a
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	498	value of either <span class="emphasis"><em>True</em></span> or <span class="emphasis"><em>False</em></span> (Note the capitalizations).</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	499	<p><a name="ch2intro_55"></a>Let us look at examples:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	500	<pre class="programlisting">>>> t = True
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	501	>>> f = not t
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	502	>>> print f
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	503	False
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	504	>>> f or t
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	505	True
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	506	>>> f and t
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	507	False</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	508	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	509	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	510	<div class="section" title="5. The while loop">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	511	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	512	<a name="id2632223"></a>5. The <span class="strong"><strong>while</strong></span> loop</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	513	<p><a name="ch2intro_56"></a>The Python <span class="strong"><strong>while</strong></span> loop is similar to the C/C++ while loop. The syntax is as
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	514	follows:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	515	<pre class="programlisting">statement 0
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	516	while condition:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	517	statement 1 #while block
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	518	statement 2 #while block
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	519	statement 3 #outside the while block.</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	520	<p><a name="ch2intro_57"></a>Let us look at an example:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	521	<pre class="programlisting">>>> x = 1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	522	>>> while x <= 5:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	523	... print x
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	524	... x += 1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	525	...
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	526	1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	527	2
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	528	3
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	529	4
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	530	5</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	531	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	532	<div class="section" title="6. The if conditional">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	533	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	534	<a name="id2632260"></a>6. The <span class="strong"><strong>if</strong></span> conditional</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	535	<p><a name="ch2intro_58"></a>The Python <span class="strong"><strong>if</strong></span> block provides the conditional execution of statements.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	536	If the condition evaluates as true the block of statements defined under the if
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	537	block are executed.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	538	<p><a name="ch2intro_59"></a>If the first block is not executed on account of the condition not being satisfied,
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	539	the set of statements in the <span class="strong"><strong>else</strong></span> block are executed.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	540	<p><a name="ch2intro_5a"></a>The <span class="strong"><strong>elif</strong></span> block provides the functionality of evaluation of multiple conditions
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	541	as shown in the example.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	542	<p><a name="ch2intro_5b"></a>The syntax is as follows:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	543	<pre class="programlisting">if condition :
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	544	statement_1
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	545	statement_2
1 672eaaab9204 Added some new html files that failed earlier during change from rst amit@thunder parents: 0 diff changeset	546
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	547	elif condition:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	548	statement_3
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	549	statement_4
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	550	else:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	551	statement_5
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	552	statement_6</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	553	<p><a name="ch2intro_5c"></a>Let us look at an example:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	554	<pre class="programlisting">>>> n = raw_input("Input a number:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	555	>>> if n < 0:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	556	print n," is negative"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	557	elif n > 0:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	558	print n," is positive"
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	559	else:
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	560	print n, " is 0"</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	561	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	562	<div class="section" title="7. raw_input()">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	563	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	564	<a name="id2632330"></a>7. <span class="strong"><strong>raw_input()</strong></span>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	565	</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	566	<p><a name="ch2intro_5d"></a>In the previous example we saw the call to the raw_input() subroutine.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	567	The <span class="strong"><strong>raw_input()</strong></span> method is used to take user inputs through the console.
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	568	Unlike <span class="strong"><strong>input()</strong></span> which assumes the data entered by the user as a standard python
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	569	expression, <span class="strong"><strong>raw_input()</strong></span> treats all the input data as raw data and converts
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	570	everything into a string. To illustrate this let us look at an example.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	571	<pre class="programlisting">>>> input("Enter a number thats a palindrome:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	572	Enter a number thats a palindrome:121
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	573	121
0 8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	574
24 10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	575	>>> input("Enter your name:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	576	Enter your name:PythonFreak
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	577	Traceback (most recent call last):
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	578	File "<stdin>", line 1, in <module>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	579	File "<string>", line 1, in <module>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	580	NameError: name 'PythonFreak' is not defined</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	581	<p><a name="ch2intro_5e"></a>As shown above the <span class="strong"><strong>input()</strong></span> assumes that the data entered is a valid Python
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	582	expression. In the first call it prompts for an integer input and when entered
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	583	it accepts the integer as an integer, whereas in the second call, when the string
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	584	is entered without the quotes, <span class="strong"><strong>input()</strong></span> assumes that the entered data is a valid
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	585	Python expression and hence it raises and exception saying PythonFreak is not
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	586	defined.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	587	<pre class="programlisting">>>> input("Enter your name:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	588	Enter your name:'PythonFreak'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	589	'PythonFreak'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	590	>>></pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	591	<p><a name="ch2intro_5f"></a>Here the name is accepted because its entered as a string (within quotes). But
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	592	its unreasonable to go on using quotes each time a string is entered. Hence the
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	593	alternative is to use <span class="strong"><strong>raw_input()</strong></span>.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	594	<p><a name="ch2intro_60"></a>Let us now look at how <span class="strong"><strong>raw_input()</strong></span> operates with an example.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	595	<pre class="programlisting">>>> raw_input("Enter your name:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	596	Enter your name:PythonFreak
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	597	'PythonFreak'</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	598	<p><a name="ch2intro_61"></a>Observe that the <span class="strong"><strong>raw_input()</strong></span> is converting it into a string all by itself.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	599	<pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	600	Enter a number thats a palindrome:121
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	601	'121'</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	602	<p><a name="ch2intro_62"></a>Observe that <span class="strong"><strong>raw_input()</strong></span> is converting the integer 121 also to a string as
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	603	'121'. Let us look at another example:</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	604	<pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	605	Enter a number thats a palindrome:121
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	606	>>> pal + 2
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	607	Traceback (most recent call last):
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	608	File "<stdin>", line 1, in <module>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	609	TypeError: cannot concatenate 'str' and 'int' objects
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	610	>>> pal
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	611	'121'</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	612	<p><a name="ch2intro_63"></a>Observe here that the variable <span class="emphasis"><em>pal</em></span> is a string and hence integer operations
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	613	cannot be performed on it. Hence the exception is raised.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	614	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	615	<div class="section" title="8. int() method">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	616	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	617	<a name="id2632484"></a>8. <span class="strong"><strong>int()</strong></span> method</h2></div></div></div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	618	<p><a name="ch2intro_64"></a>Generally for computing purposes, the data used is not strings or raw data but
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	619	on integers, floats and similar mathematical data structures. The data obtained
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	620	from <span class="strong"><strong>raw_input()</strong></span> is raw data in the form of strings. In order to obtain integers
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	621	from strings we use the method <span class="strong"><strong>int()</strong></span>.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	622	<p><a name="ch2intro_65"></a>Let us look at an example.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	623	<pre class="programlisting">>>> intpal = int(pal)
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	624	>>> intpal
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	625	121</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	626	<p><a name="ch2intro_66"></a>In the previous example it was observed that <span class="emphasis"><em>pal</em></span> was a string variable. Here
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	627	using the <span class="strong"><strong>int()</strong></span> method the string <span class="emphasis"><em>pal</em></span> was converted to an integer variable.</p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	628	<p><a name="ch2intro_67"></a><span class="emphasis"><em>Try This Yourself:</em></span></p>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	629	<pre class="programlisting">>>> stringvar = raw_input("Enter a name:")
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	630	Enter a name:Guido Van Rossum
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	631	>>> stringvar
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	632	'Guido Van Rossum'
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	633	>>> numvar = int(stringvar)</pre>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	634	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	635	</div>
10074d1357ff Some changes after the horrible problem of writing the same ch9 on all the html pages amit@thunder parents: 16 diff changeset	636	</div></body>
0 8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	637	</html>

author	amit@thunder
	Mon, 22 Feb 2010 22:38:51 +0530
changeset 24	10074d1357ff
parent 16	2e3d2cadbcb6
child 25	ed38dd9bdb50
permissions	-rw-r--r--