SEES-hacks: web/html/backup/ch01-intro.html@672eaaab9204 (annotated)

0 8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	1	<html>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	2	<head>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	3	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	4	<title>Basic Python</title>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	5	<link rel="stylesheet" href="/review/support/styles.css" type="text/css">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	6	<meta name="generator" content="DocBook XSL Stylesheets V1.74.3">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	7	<link rel="shortcut icon" type="image/png" href="/review/support/figs/favicon.png">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	8	<script type="text/javascript" src="/review/support/jquery-min.js"></script>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	9	<script type="text/javascript" src="/review/support/form.js"></script>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	10	<script type="text/javascript" src="/review/support/hsbook.js"></script>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	11	</head>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	12	<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	13	<!--<div class="navheader">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	14	<table width="100%" summary="Navigation header">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	15	<tr><th colspan="3" align="center">Basic Python</th></tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	16	<tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	17	<td width="20%" align="left">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	18
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	19	<th width="60%" align="center"> </th>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	20	<td width="20%" align="right"> </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	21	</tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	22	</table>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	23	<hr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	24	</div> -->
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	25
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	26	<div class="chapter" lang="en" id="chap_intro">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	27	<div class="article" title="Basic Python">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	28	<div class="titlepage">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	29	<div><div><h2 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	30	<a name="id2988867"></a>Basic Python</h2></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	31	<hr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	32	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	33	<div class="toc">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	34	<p><b>Table of Contents</b></p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	35	<dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	36	<dt><span class="section"><a href="#introduction">1. Introduction</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	37	<dt><span class="section"><a href="#the-python-interpreter">2. The Python Interpreter</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	38	<dd><dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	39	<dt><span class="section"><a href="#the-interactive-interpreter">2.1. The Interactive Interpreter</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	40	<dt><span class="section"><a href="#ipython-an-enhanced-interactive-python-interpreter">2.2.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	41	<span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	42	</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	43	</dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	44	<dt><span class="section"><a href="#editing-and-running-a-python-file">3. Editing and running a python file</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	45	<dt><span class="section"><a href="#basic-datatypes-and-operators-in-python">4. Basic Datatypes and operators in Python</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	46	<dd><dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	47	<dt><span class="section"><a href="#numbers">4.1. Numbers</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	48	<dt><span class="section"><a href="#variables">4.2. Variables</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	49	<dt><span class="section"><a href="#strings">4.3. Strings</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	50	<dt><span class="section"><a href="#boolean">4.4. Boolean</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	51	</dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	52	<dt><span class="section"><a href="#the-while-loop">5. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	53	<span class="strong"><strong>while</strong></span> loop
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	54	</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	55	<dt><span class="section"><a href="#the-if-conditional">6. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	56	<span class="strong"><strong>if</strong></span> conditional
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	57	</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	58	<dt><span class="section"><a href="#raw_input">7. <span class="strong"><strong>raw_input()</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	59	</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	60	<dt><span class="section"><a href="#int-method">8.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	61	<span class="strong"><strong>int()</strong></span> method
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	62	</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	63	</dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	64	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	65	<p id="x_38"></a>This document is intended to be handed out at the end of the workshop. It has been designed for Engineering students who are Python beginners and have basic programming skills. The focus is on basic numerics and plotting using Python.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	66	<p id="x_39"></a>The system requirements:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	67	<div class="itemizedlist"><ul class="itemizedlist" type="*">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	68	<li class="listitem" style="list-style-type: *"><p id="x_3a"></a>Python - version 2.5.x or newer.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	69	<li class="listitem" style="list-style-type: *"><p id="x_3b"></a>IPython</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	70	<li class="listitem" style="list-style-type: *"><p id="x_3c"></a>Text editor - scite, vim, emacs or whatever you are comfortable with.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	71	</ul></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	72	<div class="section" title="1. Introduction">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	73	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	74	<a name="introduction"></a>1. Introduction</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	75	<p id="x_3d"></a>The Python programming language was created by a dutch named Guido van Rossum. The idea of Python was conceived in December 1989. The name Python has nothing to do with the reptilian, but its been named after the 70s comedy series "Monty Python's Flying Circus", since it happens to be Guido's favourite TV series.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	76	<p id="x_3e"></a>Current stable version of Python is 2.6.x, although Python 3.0 is also the stable version, it is not backwards compatible with the previous versions and is hence not entirely popular at the moment. This material will focus on the 2.6.x series.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	77	<p id="x_3f"></a>Python is licensed under the Python Software Foundation License (PSF License) which is GPL compatible Free Software license (excepting license version 1.6 and 2.0) It is a no strings attached license, which means the source code is free to modify and redistribute.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	78	<p id="x_40"></a>The Python docs define Python as "Python is an interpreted, object-oriented, high-level programming language with dynamic semantics." A more detailed summary can be found at
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	79	<a class="ulink" href="http://www.python.org/doc/essays/blurb.html" target="_top">http://www.python.org/doc/essays/blurb.html</a>. Python is a language that has been designed to help the programmer concentrate on solving the problem at hand and not worry about the programming language idiosyncrasies.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	80	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	81	<p id="x_41"></a>Python is a highly cross platform compatible language on account of it being an interpreted language. It is highly scalable and hence has been adapted to run on the Nokia 60 series phones. Python has been designed to be readable and easy to use</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	82	<p id="x_42"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	83	<span class="strong"><strong>Resources available for reference</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	84	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	85	<div class="itemizedlist"><ul class="itemizedlist" type="*">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	86	<li class="listitem" style="list-style-type: *"><p id="x_43"></a>Web:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	87	<a class="ulink" href="http://www.python.org" target="_top">http://www.python.org</a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	88	</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	89	<li class="listitem" style="list-style-type: *"><p id="x_44"></a>Doc:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	90	<a class="ulink" href="http://www.python.org/doc" target="_top">http://www.python.org/doc</a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	91	</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	92	<li class="listitem" style="list-style-type: *"><p id="x_45"></a>Free Tutorials:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	93	<span class="emphasis"><em> Official Python Tutorial:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	94	<a class="ulink" href="http://docs.python.org/tut/tut.html" target="_top">http://docs.python.org/tut/tut.html</a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	95	</em></span> Byte of Python:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	96	<a class="ulink" href="http://www.byteofpython.info" target="_top">http://www.byteofpython.info</a>/ * Dive into Python:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	97	<a class="ulink" href="http://diveintopython.org" target="_top">http://diveintopython.org</a>/
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	98	</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	99	</ul></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	100	<p id="x_46"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	101	<span class="strong"><strong>Advantages of Python - Why Python??</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	102	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	103	<div class="itemizedlist"><ul class="itemizedlist" type="*">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	104	<li class="listitem" style="list-style-type: *"><p id="x_47"></a>Python has been designed for readability and ease of use. Its been designed in such a fashion that it imposes readability on the programmer. Python does away with the braces and the semicolons and instead implements code blocks based on indentation, thus enhancing readability.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	105	<li class="listitem" style="list-style-type: *"><p id="x_48"></a>Python is a high level, interpreted, modular and object oriented language. Python performs memory management on its own, thus the programmer need not bother about allocating and deallocating memory to variables. Python provides extensibility by providing modules which can be easily imported similar to headers in C and packages in Java. Python is object oriented and hence provides all the object oriented characteristics such as inheritance, encapsulation and polymorphism.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	106	<li class="listitem" style="list-style-type: *"><p id="x_49"></a>Python offers a highly powerful interactive programming interface in the form of the 'Interactive Interpreter' which will be discussed in more detail in the following sections.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	107	<li class="listitem" style="list-style-type: *"><p id="x_4a"></a>Python provides a rich standard library and an extensive set of modules. The power of Python modules can be seen in this slightly exaggerated cartoon
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	108	<a class="ulink" href="http://xkcd.com/353" target="_top">http://xkcd.com/353</a>/
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	109	</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	110	<li class="listitem" style="list-style-type: *"><p id="x_4b"></a>Python interfaces well with most other programming languages such as C, C++ and FORTRAN.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	111	</ul></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	112	<p id="x_4c"></a>Although, Python has one setback. Python is not fast as some of the compiled languages like C or C++. Yet, the amount of flexibility and power more than make up for this setback.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	113	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	114	<div class="section" title="2. The Python Interpreter">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	115	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	116	<a name="the-python-interpreter"></a>2. The Python Interpreter</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	117	<div class="section" title="2.1. The Interactive Interpreter">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	118	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	119	<a name="the-interactive-interpreter"></a>2.1. The Interactive Interpreter</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	120	<p id="x_4d"></a>Typing
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	121	<span class="emphasis"><em>python</em></span> at the shell prompt on any standard Unix/Gnu-Linux system and hitting the enter key fires up the Python 'Interactive Interpreter'. The Python interpreter is one of the most integral features of Python. The prompt obtained when the interactive interpreter is similar to what is shown below. The exact appearance might differ based on the version of Python being used. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	122	<code class="literal">>>></code> thing shown is the python prompt. When something is typed at the prompt and the enter key is hit, the python interpreter interprets the command entered and performs the appropriate action. All the examples presented in this document are to be tried hands on, on the interactive interpreter.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	123	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	124	<pre class="programlisting">Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	125	[GCC 4.3.2] on linux2
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	126	Type "help", "copyright", "credits" or "license" for more information.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	127	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	128
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	129	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	130	<p id="x_4e"></a>Lets try with an example, type
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	131	<code class="literal">print 'Hello, World!'</code> at the prompt and hit the enter key.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	132	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	133	<pre class="programlisting">>>> print 'Hello, World!'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	134	Hello, World!
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	135
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	136	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	137	<p id="x_4f"></a>This example was quite straight forward, and thus we have written our first line of Python code. Now let us try typing something arbitrary at the prompt. For example:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	138	<pre class="programlisting">>>> arbit word
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	139	File "<stdin>", line 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	140	arbit word
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	141	^
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	142	SyntaxError: invalid syntax
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	143	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	144
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	145	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	146	<p id="x_50"></a>The interpreter gave an error message saying that 'arbit word' was invalid syntax which is valid. The interpreter is an amazing tool when learning to program in Python. The interpreter provides a help function that provides the necessary documentation regarding all Python syntax, constructs, modules and objects. Typing
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	147	<span class="emphasis"><em>help()</em></span> at the prompt gives the following output:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	148	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	149	<pre class="programlisting">>>> help()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	150
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	151	Welcome to Python 2.5! This is the online help utility.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	152
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	153	If this is your first time using Python, you should definitely check out
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	154	the tutorial on the Internet at http://www.python.org/doc/tut/.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	155
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	156	Enter the name of any module, keyword, or topic to get help on writing
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	157	Python programs and using Python modules. To quit this help utility and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	158	return to the interpreter, just type "quit".
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	159
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	160	To get a list of available modules, keywords, or topics, type "modules",
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	161	"keywords", or "topics". Each module also comes with a one-line summary
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	162	of what it does; to list the modules whose summaries contain a given word
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	163	such as "spam", type "modules spam".
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	164
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	165	help>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	166
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	167
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	168	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	169	<p id="x_51"></a>As mentioned in the output, entering the name of any module, keyword or topic will provide the documentation and help regarding the same through the online help utility. Pressing
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	170	<span class="emphasis"><em>Ctrl+d</em></span> exits the help prompt and returns to the python prompt.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	171	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	172	<p id="x_52"></a>Let us now try a few examples at the python interpreter.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	173	<p id="x_53"></a>Eg 1:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	174	<pre class="programlisting">>>> print 'Hello, python!'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	175	Hello, python!
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	176	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	177
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	178	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	179	<p id="x_54"></a>Eg 2:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	180	<pre class="programlisting">>>> print 4321*567890
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	181	2453852690
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	182	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	183
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	184	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	185	<p id="x_55"></a>Eg 3:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	186	<pre class="programlisting">>>> 4321*567890
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	187	2453852690L
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	188	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	189
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	190	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	191	<pre class="programlisting">Note: Notice the 'L' at the end of the output. The 'L' signifies that the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	192	output of the operation is of type long. It was absent in the previous
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	193	example because we used the print statement. This is because print formats
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	194	the output before displaying.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	195
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	196	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	197	<p id="x_56"></a>Eg 4:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	198	<pre class="programlisting">>>> big = 12345678901234567890 ** 3
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	199	>>> print big
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	200	1881676372353657772490265749424677022198701224860897069000
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	201	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	202
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	203	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	204	<pre class="programlisting">This example is to show that unlike in C or C++ there is no limit on the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	205	value of an integer.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	206
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	207	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	208	<p id="x_57"></a>Try this on the interactive interpreter:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	209	<code class="literal">import this</code>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	210	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	211	<p id="x_58"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	212	<span class="emphasis"><em>Hint: The output gives an idea of Power of Python</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	213	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	214	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	215	<div class="section" title="2.2. ipython - An enhanced interactive Python interpreter">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	216	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	217	<a name="ipython-an-enhanced-interactive-python-interpreter"></a>2.2.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	218	<span class="emphasis"><em>ipython</em></span> - An enhanced interactive Python interpreter
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	219	</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	220	<p id="x_59"></a>The power and the importance of the interactive interpreter was the highlight of the previous section. This section provides insight into the enhanced interpreter with more advanced set of features called
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	221	<span class="strong"><strong>ipython</strong></span>. Entering
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	222	<span class="emphasis"><em>ipython</em></span> at the shell prompt fires up the interactive interpreter.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	223	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	224	<pre class="programlisting">$ ipython
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	225	Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	226	Type "copyright", "credits" or "license" for more information.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	227
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	228	IPython 0.8.4 -- An enhanced Interactive Python.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	229	? -> Introduction and overview of IPython's features.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	230	%quickref -> Quick reference.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	231	help -> Python's own help system.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	232	object? -> Details about 'object'. ?object also works, ?? prints more.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	233
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	234	In [1]:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	235
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	236	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	237	<p id="x_5a"></a>This is the output obtained upon firing ipython. The exact appearance may change based on the Python version installed. The following are some of the various features provided by
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	238	<span class="strong"><strong>ipython</strong></span>:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	239	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	240	<div class="variablelist"><dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	241	<dt><span class="term"></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	242	<dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	243	<p></p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	244	<p id="x_5b"></a>Suggestions - ipython provides suggestions of the possible methods and operations available for the given python object.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	245	</dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	246	</dl></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	247	<p id="x_5c"></a>Eg 5:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	248	<pre class="programlisting">In [4]: a = 6
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	249
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	250	In [5]: a.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	251	a.__abs__ a.__divmod__ a.__index__ a.__neg__ a.__rand__ a.__rmod__ a.__rxor__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	252	a.__add__ a.__doc__ a.__init__ a.__new__ a.__rdiv__ a.__rmul__ a.__setattr__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	253	a.__and__ a.__float__ a.__int__ a.__nonzero__ a.__rdivmod__ a.__ror__ a.__str__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	254	a.__class__ a.__floordiv__ a.__invert__ a.__oct__ a.__reduce__ a.__rpow__ a.__sub__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	255	a.__cmp__ a.__getattribute__ a.__long__ a.__or__ a.__reduce_ex__ a.__rrshift__ a.__truediv__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	256	a.__coerce__ a.__getnewargs__ a.__lshift__ a.__pos__ a.__repr__ a.__rshift__ a.__xor__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	257	a.__delattr__ a.__hash__ a.__mod__ a.__pow__ a.__rfloordiv__ a.__rsub__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	258	a.__div__ a.__hex__ a.__mul__ a.__radd__ a.__rlshift__ a.__rtruediv__
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	259
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	260	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	261	<p id="x_5d"></a>In this example, we initialized 'a' (a variable - a concept that will be discussed in the subsequent sections.) to 6. In the next line when the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	262	<span class="emphasis"><em>tab</em></span> key is pressed after typing '
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	263	<span class="emphasis"><em>a.</em></span>' ipython displays the set of all possible methods that are applicable on the object 'a' (an integer in this context). Ipython provides many such datatype specific features which will be presented in the further sections as and when the datatypes are introduced.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	264	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	265	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	266	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	267	<div class="section" title="3. Editing and running a python file">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	268	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	269	<a name="editing-and-running-a-python-file"></a>3. Editing and running a python file</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	270	<p id="x_5e"></a>The previous sections focused on the use of the interpreter to run python code. While the interpeter is an excellent tool to test simple solutions and experiment with small code snippets, its main disadvantage is that everything written in the interpreter is lost once its quit. Most of the times a program is used by people other than the author. So the programs have to be available in some form suitable for distribution, and hence they are written in files. This section will focus on editing and running python files. Start by opening a text editor ( it is recommended you choose one from the list at the top of this page ). In the editor type down python code and save the file with an extension
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	271	<span class="strong"><strong>.py</strong></span> (python files have an extension of .py). Once done with the editing, save the file and exit the editor.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	272	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	273	<p id="x_5f"></a>Let us look at a simple example of calculating the gcd of 2 numbers using Python:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	274	<p id="x_60"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	275	<span class="strong"><strong>Creating the first python script(file)</strong></span> :
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	276	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	277	<pre class="programlisting">$ emacs gcd.py
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	278	def gcd(x,y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	279	if x % y == 0:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	280	return y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	281	return gcd(y, x%y)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	282
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	283	print gcd(72, 92)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	284
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	285	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	286	<p id="x_61"></a>To run the script, open the shell prompt, navigate to the directory that contains the python file and run
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	287	<code class="literal">python <filename.py></code> at the prompt ( in this case filename is gcd.py )
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	288	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	289	<p id="x_62"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	290	<span class="strong"><strong>Running the python script</strong></span> :
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	291	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	292	<pre class="programlisting">$ python gcd.py
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	293	4
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	294	$
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	295
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	296	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	297	<p id="x_63"></a>Another method to run a python script would be to include the line</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	298	<p id="x_64"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	299	<code class="literal">#! /usr/bin/python</code>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	300	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	301	<p id="x_65"></a>at the beginning of the python file and then make the file executable by</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	302	<p id="x_66"></a>$ chmod a+x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	303	<span class="emphasis"><em>filename.py</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	304	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	305	<p id="x_67"></a>Once this is done, the script can be run as a standalone program as follows:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	306	<p id="x_68"></a>$ ./
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	307	<span class="emphasis"><em>filename.py</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	308	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	309	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	310	<div class="section" title="4. Basic Datatypes and operators in Python">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	311	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	312	<a name="basic-datatypes-and-operators-in-python"></a>4. Basic Datatypes and operators in Python</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	313	<p id="x_69"></a>Python provides the following set of basic datatypes.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	314	<div class="blockquote"><blockquote class="blockquote"><div class="itemizedlist"><ul class="itemizedlist" type="*">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	315	<li class="listitem" style="list-style-type: *"><p id="x_6a"></a>Numbers: int, float, long, complex</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	316	<li class="listitem" style="list-style-type: *"><p id="x_6b"></a>Strings</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	317	<li class="listitem" style="list-style-type: *"><p id="x_6c"></a>Boolean</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	318	</ul></div></blockquote></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	319	<div class="section" title="4.1. Numbers">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	320	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	321	<a name="numbers"></a>4.1. Numbers</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	322	<p id="x_6d"></a>Numbers were introduced in the examples presented in the interactive interpreter section. Numbers include types as mentioned earlier viz., int (integers), float (floating point numbers), long (large integers), complex (complex numbers with real and imaginary parts). Python is not a strongly typed language, which means the type of a variable need not mentioned during its initialization. Let us look at a few examples.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	323	<p id="x_6e"></a>Eg 6:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	324	<pre class="programlisting">>>> a = 1 #here a is an integer variable
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	325
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	326	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	327	<p id="x_6f"></a>Eg 7:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	328	<pre class="programlisting">>>> lng = 122333444455555666666777777788888888999999999 #here lng is a variable of type long
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	329	>>> lng
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	330	122333444455555666666777777788888888999999999L #notice the trailing 'L'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	331	>>> print lng
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	332	122333444455555666666777777788888888999999999 #notice the absence of the trailing 'L'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	333	>>> lng+1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	334	122333444455555666666777777788888889000000000L
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	335
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	336
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	337	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	338	<p id="x_70"></a>Long numbers are the same as integers in almost all aspects. They can be used in operations just like integers and along with integers without any distinction. The only distinction comes during type checking (which is not a healthy practice). Long numbers are tucked with a trailing 'L' just to signify that they are long. Notice that in the example just lng at the prompt displays the value of the variable with the 'L' whereas
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	339	<code class="literal">print lng</code> displays without the 'L'. This is because print formats the output before printing. Also in the example, notice that adding an integer to a long does not give any errors and the result is as expected. So for all practical purposes longs can be treated as ints.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	340	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	341	<p id="x_71"></a>Eg 8:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	342	<pre class="programlisting">>>> fl = 3.14159 #fl is a float variable
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	343	>>> e = 1.234e-4 #e is also a float variable, specified in the exponential form
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	344	>>> a = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	345	>>> b = 2
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	346	>>> a/b #integer division
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	347	0
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	348	>>> a/fl #floating point division
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	349	0.31831015504887655
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	350	>>> e/fl
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	351	3.9279473133031364e-05
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	352
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	353
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	354	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	355	<p id="x_72"></a>Floating point numbers, simply called floats are real numbers with a decimal point. The example above shows the initialization of a float variable. Shown also in this example is the difference between integer division and floating point division. 'a' and 'b' here are integer variables and hence the division gives 0 as the quotient. When either of the operands is a float, the operation is a floating point division, and the result is also a float as illustrated.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	356	<p id="x_73"></a>Eg 9:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	357	<pre class="programlisting">>>> cplx = 3 + 4j #cplx is a complex variable
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	358	>>> cplx
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	359	(3+4j)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	360	>>> print cplx.real #prints the real part of the complex number
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	361	3.0
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	362	>>> print cplx.imag #prints the imaginary part of the complex number
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	363	4.0
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	364	>>> print cplx*fl #multiplies the real and imag parts of the complex number with the multiplier
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	365	(9.42477+12.56636j)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	366	>>> abs(cplx) #returns the absolute value of the complex number
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	367	5.0
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	368
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	369	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	370	<p id="x_74"></a>Python provides a datatype for complex numbers. Complex numbers are initialized as shown in the example above. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	371	<span class="emphasis"><em>real</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	372	<span class="emphasis"><em>imag</em></span> operators return the real and imaginary parts of the complex number as shown. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	373	<span class="emphasis"><em>abs()</em></span> returns the absolute value of the complex number.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	374	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	375	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	376	<div class="section" title="4.2. Variables">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	377	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	378	<a name="variables"></a>4.2. Variables</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	379	<p id="x_75"></a>Variables are just names that represent a value. Variables have already been introduced in the various examples from the previous sections. Certain rules about using variables:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	380	<div class="blockquote"><blockquote class="blockquote"><div class="itemizedlist"><ul class="itemizedlist" type="*">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	381	<li class="listitem" style="list-style-type: *"><p id="x_76"></a>Variables have to be initialized or assigned a value before being used.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	382	<li class="listitem" style="list-style-type: *"><p id="x_77"></a>Variable names can consist of letters, digits and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	383	<a class="link" href="">underscores</a> .
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	384	</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	385	<li class="listitem" style="list-style-type: *"><p id="x_78"></a>Variable names cannot begin with digits, but can contain digits in them.</p></li>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	386	</ul></div></blockquote></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	387	<p id="x_79"></a>In reference to the previous section examples, 'a', 'b', 'lng', 'fl', 'e' and 'cplx' are all variables of various datatypes.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	388	<pre class="programlisting">Note: Python is not a strongly typed language and hence an integer variable can at a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	389	later stage be used as a float variable as well.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	390
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	391	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	392	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	393	<div class="section" title="4.3. Strings">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	394	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	395	<a name="strings"></a>4.3. Strings</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	396	<p id="x_7a"></a>Strings are one of the essential data structures of any programming language. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	397	<code class="literal">print "Hello, World!"</code> program was introduced in the earlier section, and the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	398	<span class="emphasis"><em>"Hello, World!"</em></span> in the print statement is a string. A string is basically a set of characters. Strings can be represented in various ways shown below:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	399	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	400	<pre class="programlisting">s = 'this is a string' # a string variable can be represented using single quotes
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	401	s = 'This one has "quotes" inside!' # The string can have quotes inside it as shown
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	402	s = "I have 'single-quotes' inside!"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	403	l = "A string spanning many lines\
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	404	one more line\
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	405	yet another" # a string can span more than a single line.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	406	t = """A triple quoted string does # another way of representing multiline strings.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	407	not need to be escaped at the end and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	408	"can have nested quotes" etc."""
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	409
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	410	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	411	<p id="x_7b"></a>Try the following on the interpreter:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	412	<code class="literal">s = 'this is a string with 'quotes' of similar kind'</code>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	413	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	414	<p id="x_7c"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	415	<span class="strong"><strong>Exercise: How to use single quotes within single quotes in a string as shown in the above example without getting an error?</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	416	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	417	<div class="section" title="4.3.1. String operations">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	418	<div class="titlepage"><div><div><h4 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	419	<a name="string-operations"></a>4.3.1. String operations</h4></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	420	<p id="x_7d"></a>A few basic string operations are presented here.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	421	<p id="x_7e"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	422	<span class="strong"><strong>String concatenation</strong></span> String concatenation is done by simple addition of two strings.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	423	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	424	<pre class="programlisting">>>> x = 'Hello'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	425	>>> y = ' Python'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	426	>>> print x+y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	427	Hello Python
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	428
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	429	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	430	<p id="x_7f"></a> <span class="emphasis"><em>Try this yourself:</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	431	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	432	<pre class="programlisting">>>> somenum = 13
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	433	>>> print x+somenum
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	434
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	435	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	436	<p id="x_80"></a>The problem with the above example is that here a string variable and an integer variable are trying to be concantenated. To obtain the desired result from the above example the str(), repr() and the `` can be used.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	437	<p id="x_81"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	438	<span class="strong"><strong>str()</strong></span> simply converts a value to a string in a reasonable form.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	439	<span class="strong"><strong>repr()</strong></span> creates a string that is a representation of the value.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	440	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	441	<p id="x_82"></a>The difference can be seen in the example shown below:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	442	<pre class="programlisting">>>> str(1000000000000000000000000000000000000000000000000L)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	443	'1000000000000000000000000000000000000000000000000'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	444	>>> repr(1000000000000000000000000000000000000000000000000L)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	445	'1000000000000000000000000000000000000000000000000L'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	446
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	447	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	448	<p id="x_83"></a>It can be observed that the 'L' in the long value shown was omitted by str(), whereas repr() converted that into a string too. An alternative way of using repr(value) is `
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	449	<code class="literal">value</code>`.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	450	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	451	<p id="x_84"></a>A few more examples:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	452	<pre class="programlisting">>>> x = "Let's go \nto Pycon"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	453	>>> print x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	454	Let's go
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	455	to Pycon
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	456
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	457	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	458	<p id="x_85"></a>In the above example, notice that the '\n'(newline) character is formatted and the string is printed on two lines. The strings discussed until now were normal strings. Other than these there are two other types of strings namely, raw strings and unicode strings.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	459	<p id="x_86"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	460	<span class="strong"><strong>Raw strings</strong></span> are strings which are unformatted, that is the backslashes(\) are not parsed and are left as it is in the string. Raw strings are represented with an 'r' at the start of a string. Let us look at an example
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	461	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	462	<pre class="programlisting">>>> x = r"Let's go \nto Pycon"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	463	>>> print x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	464	Let's go \nto Pycon
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	465
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	466	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	467	<p id="x_87"></a>Note: The '\n' is not being parsed into a new line and is left as it is.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	468	<p id="x_88"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	469	<span class="emphasis"><em>Try this yourself:</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	470	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	471	<pre class="programlisting">>>> x = r"Let's go to Pycon\"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	472
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	473	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	474	<p id="x_89"></a> <span class="strong"><strong>Unicode strings</strong></span> are strings where the characters are Unicode characters as opposed to ASCII characters. Unicode strings are represented with a 'u' at the start of the string. Let us look at an example:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	475	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	476	<pre class="programlisting">>>> x = u"Let's go to Pycon!"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	477	>>> print x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	478	Let's go to Pycon!
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	479
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	480	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	481	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	482	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	483	<div class="section" title="4.4. Boolean">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	484	<div class="titlepage"><div><div><h3 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	485	<a name="boolean"></a>4.4. Boolean</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	486	<p id="x_8a"></a>Python also provides special Boolean datatype. A boolean variable can assume a value of either
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	487	<span class="emphasis"><em>True</em></span> or
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	488	<span class="emphasis"><em>False</em></span> (Note the capitalizations).
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	489	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	490	<p id="x_8b"></a>Let us look at examples:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	491	<pre class="programlisting">>>> t = True
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	492	>>> f = not t
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	493	>>> print f
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	494	False
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	495	>>> f or t
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	496	True
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	497	>>> f and t
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	498	False
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	499
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	500	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	501	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	502	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	503	<div class="section" title="5. The while loop">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	504	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	505	<a name="the-while-loop"></a>5. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	506	<span class="strong"><strong>while</strong></span> loop
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	507	</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	508	<p id="x_8c"></a>The Python
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	509	<span class="strong"><strong>while</strong></span> loop is similar to the C/C++ while loop. The syntax is as follows:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	510	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	511	<pre class="programlisting">statement 0
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	512	while condition:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	513	statement 1 #while block
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	514	statement 2 #while block
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	515	statement 3 #outside the while block.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	516
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	517	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	518	<p id="x_8d"></a>Let us look at an example:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	519	<pre class="programlisting">>>> x = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	520	>>> while x <= 5:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	521	... print x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	522	... x += 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	523	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	524	1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	525	2
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	526	3
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	527	4
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	528	5
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	529
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	530	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	531	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	532	<div class="section" title="6. The if conditional">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	533	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	534	<a name="the-if-conditional"></a>6. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	535	<span class="strong"><strong>if</strong></span> conditional
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	536	</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	537	<p id="x_8e"></a>The Python
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	538	<span class="strong"><strong>if</strong></span> block provides the conditional execution of statements. If the condition evaluates as true the block of statements defined under the if block are executed.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	539	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	540	<p id="x_8f"></a>If the first block is not executed on account of the condition not being satisfied, the set of statements in the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	541	<span class="strong"><strong>else</strong></span> block are executed.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	542	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	543	<p id="x_90"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	544	<span class="strong"><strong>elif</strong></span> block provides the functionality of evaluation of multiple conditions as shown in the example.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	545	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	546	<p id="x_91"></a>The syntax is as follows:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	547	<pre class="programlisting">if condition :
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	548	statement_1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	549	statement_2
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	550
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	551	elif condition:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	552	statement_3
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	553	statement_4
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	554	else:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	555	statement_5
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	556	statement_6
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	557
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	558	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	559	<p id="x_92"></a>Let us look at an example:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	560	<pre class="programlisting">>>> n = raw_input("Input a number:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	561	>>> if n < 0:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	562	print n," is negative"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	563	elif n > 0:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	564	print n," is positive"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	565	else:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	566	print n, " is 0"
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	567
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	568	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	569	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	570	<div class="section" title="7. raw_input()">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	571	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	572	<a name="raw_input"></a>7. <span class="strong"><strong>raw_input()</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	573	</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	574	<p id="x_93"></a>In the previous example we saw the call to the raw_input() subroutine. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	575	<span class="strong"><strong>raw_input()</strong></span> method is used to take user inputs through the console. Unlike
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	576	<span class="strong"><strong>input()</strong></span> which assumes the data entered by the user as a standard python expression,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	577	<span class="strong"><strong>raw_input()</strong></span> treats all the input data as raw data and converts everything into a string. To illustrate this let us look at an example.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	578	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	579	<pre class="programlisting">>>> input("Enter a number thats a palindrome:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	580	Enter a number thats a palindrome:121
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	581	121
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	582
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	583	>>> input("Enter your name:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	584	Enter your name:PythonFreak
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	585	Traceback (most recent call last):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	586	File "<stdin>", line 1, in <module>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	587	File "<string>", line 1, in <module>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	588	NameError: name 'PythonFreak' is not defined
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	589
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	590	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	591	<p id="x_94"></a>As shown above the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	592	<span class="strong"><strong>input()</strong></span> assumes that the data entered is a valid Python expression. In the first call it prompts for an integer input and when entered it accepts the integer as an integer, whereas in the second call, when the string is entered without the quotes,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	593	<span class="strong"><strong>input()</strong></span> assumes that the entered data is a valid Python expression and hence it raises and exception saying PythonFreak is not defined.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	594	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	595	<pre class="programlisting">>>> input("Enter your name:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	596	Enter your name:'PythonFreak'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	597	'PythonFreak'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	598	>>>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	599
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	600	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	601	<p id="x_95"></a>Here the name is accepted because its entered as a string (within quotes). But its unreasonable to go on using quotes each time a string is entered. Hence the alternative is to use
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	602	<span class="strong"><strong>raw_input()</strong></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	603	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	604	<p id="x_96"></a>Let us now look at how
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	605	<span class="strong"><strong>raw_input()</strong></span> operates with an example.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	606	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	607	<pre class="programlisting">>>> raw_input("Enter your name:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	608	Enter your name:PythonFreak
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	609	'PythonFreak'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	610
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	611	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	612	<p id="x_97"></a>Observe that the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	613	<span class="strong"><strong>raw_input()</strong></span> is converting it into a string all by itself.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	614	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	615	<pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	616	Enter a number thats a palindrome:121
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	617	'121'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	618
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	619	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	620	<p id="x_98"></a>Observe that
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	621	<span class="strong"><strong>raw_input()</strong></span> is converting the integer 121 also to a string as '121'. Let us look at another example:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	622	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	623	<pre class="programlisting">>>> pal = raw_input("Enter a number thats a palindrome:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	624	Enter a number thats a palindrome:121
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	625	>>> pal + 2
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	626	Traceback (most recent call last):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	627	File "<stdin>", line 1, in <module>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	628	TypeError: cannot concatenate 'str' and 'int' objects
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	629	>>> pal
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	630	'121'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	631
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	632	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	633	<p id="x_99"></a>Observe here that the variable
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	634	<span class="emphasis"><em>pal</em></span> is a string and hence integer operations cannot be performed on it. Hence the exception is raised.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	635	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	636	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	637	<div class="section" title="8. int() method">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	638	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	639	<a name="int-method"></a>8.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	640	<span class="strong"><strong>int()</strong></span> method
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	641	</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	642	<p id="x_9a"></a>Generally for computing purposes, the data used is not strings or raw data but on integers, floats and similar mathematical data structures. The data obtained from
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	643	<span class="strong"><strong>raw_input()</strong></span> is raw data in the form of strings. In order to obtain integers from strings we use the method
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	644	<span class="strong"><strong>int()</strong></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	645	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	646	<p id="x_9b"></a>Let us look at an example.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	647	<pre class="programlisting">>>> intpal = int(pal)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	648	>>> intpal
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	649	121
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	650
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	651	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	652	<p id="x_9c"></a>In the previous example it was observed that
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	653	<span class="emphasis"><em>pal</em></span> was a string variable. Here using the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	654	<span class="strong"><strong>int()</strong></span> method the string
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	655	<span class="emphasis"><em>pal</em></span> was converted to an integer variable.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	656	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	657	<p id="x_9d"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	658	<span class="emphasis"><em>Try This Yourself:</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	659	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	660	<pre class="programlisting">>>> stringvar = raw_input("Enter a name:")
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	661	Enter a name:Guido Van Rossum
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	662	>>> stringvar
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	663	'Guido Van Rossum'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	664	>>> numvar = int(stringvar)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	665
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	666	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	667	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	668	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	669	<div class="navfooter">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	670	<hr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	671	<table width="100%" summary="Navigation footer">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	672	<tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	673	<td width="40%" align="left">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	674	<a accesskey="p" href="index.html">Prev</a> </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	675	<td width="20%" align="center"> </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	676	<td width="40%" align="right"> </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	677	</tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	678	<tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	679	<td width="40%" align="left" valign="top">Chapter 1. Introduction </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	680	<td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	681	<td width="40%" align="right" valign="top"> </td>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	682	</tr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	683	</table>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	684	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	685	</body>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	686	</html>

author	amit@thunder
	Fri, 05 Feb 2010 23:42:24 +0530
changeset 1	672eaaab9204
parent 0	8083d21c0020
permissions	-rwxr-xr-x