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8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	3	<title>Chapter 9. Finding and fixing mistakes</title>
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8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	16	<tr><th colspan="3" align="center">Chapter 14. Adding functionality with extensions</th></tr>
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8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	27	<div class="chapter" title="Chapter 14. Adding functionality with extensions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	28	<div class="titlepage"><div><div><h2 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	29	<a name="chap:hgext"></a>Chapter 14. Adding functionality with extensions</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	30	<div class="toc">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	31	<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	32	<dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	33	<dt><span class="sect1"><a href="adding-functionality-with-extensions.html#sec:hgext:inotify">14.1. Improve performance with the <code class="literal">inotify</code> extension</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	34	<dt><span class="sect1"><a href="adding-functionality-with-extensions.html#sec:hgext:extdiff">14.2. Flexible diff support with the <code class="literal">extdiff</code> extension</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	35	<dd><dl><dt><span class="sect2"><a href="adding-functionality-with-extensions.html#id3071699">14.2.1. Defining command aliases</a></span></dt></dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	36	<dt><span class="sect1"><a href="adding-functionality-with-extensions.html#sec:hgext:transplant">14.3. Cherrypicking changes with the <code class="literal">transplant</code> extension</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="sect1"><a href="adding-functionality-with-extensions.html#sec:hgext:patchbomb">14.4. Send changes via email with the <code class="literal">patchbomb</code> extension</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	38	<dd><dl><dt><span class="sect2"><a href="adding-functionality-with-extensions.html#id3072184">14.4.1. Changing the behavior of patchbombs</a></span></dt></dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	39	</dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	40	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	41	<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	42	<dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	43	<dt><span class="section"><a href="#default-arguments">1. Default Arguments</a></span></dt>
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="#keyword-arguments">2. Keyword Arguments</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="#parameter-packing-and-unpacking">3. Parameter Packing and Unpacking</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	46	<dt><span class="section"><a href="#nested-functions-and-scopes">4. Nested Functions and Scopes</a></span></dt>
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="#map-reduce-and-filter-functions">5. map, reduce and filter functions</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	48	<dd><dl><dt><span class="section"><a href="#list-comprehensions">5.1. List Comprehensions</a></span></dt></dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	49	</dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	50
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	51	<p id="x_74b">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	52	<span class="emphasis"><em>Functions</em></span> allow us to enclose a set of statements and call the function again and again instead of repeating the group of statements everytime. Functions also allow us to isolate a piece of code from all the other code and provides the convenience of not polluting the global variables.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	53	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	54	<p id="x_74c"<a name="x_74c"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	55	<span class="emphasis"><em>Function</em></span> in python is defined with the keyword
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	56	<span class="strong"><strong>def</strong></span> followed by the name of the function, in turn followed by a pair of parenthesis which encloses the list of parameters to the function. The definition line ends with a ':'. The definition line is followed by the body of the function intended by one block. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	57	<span class="emphasis"><em>Function</em></span> must return a value:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	58	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	59	<pre class="programlisting">def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	60	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	61	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	62	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	63
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	64	return fact
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	65
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	66	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	67	<p><a name="x_74d"></a>The code snippet above defines a function with the name factorial, takes the number for which the factorial must be computed, computes the factorial and returns the value.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	68	<p><a name="x_74e"></a>A
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	69	<span class="emphasis"><em>Function</em></span> once defined can be used or called anywhere else in the program. We call a fucntion with its name followed by a pair of parenthesis which encloses the arguments to the function.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	70	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	71	<p><a name="x_74f"></a>The value that function returns can be assigned to a variable. Let's call the above function and store the factorial in a variable:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	72	<pre class="programlisting">fact5 = factorial(5)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	73
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	74	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	75	<p><a name="x_750"></a>The value of fact5 will now be 120, which is the factorial of 5. Note that we passed 5 as the argument to the function.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	76	<p><a name="x_751"></a>It may be necessary to document what the function does, for each of the function to help the person who reads our code to understand it better. In order to do this Python allows the first line of the function body to be a string. This string is called as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	77	<span class="emphasis"><em>Documentation String</em></span> or
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	78	<span class="emphasis"><em>docstring</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	79	<span class="emphasis"><em>docstrings</em></span> prove to be very handy since there are number of tools which can pull out all the docstrings from Python functions and generate the documentation automatically from it.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	80	<span class="emphasis"><em>docstrings</em></span> for functions can be written as follows:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	81	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	82	<pre class="programlisting">def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	83	'Returns the factorial for the number n.'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	84	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	85	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	86	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	87
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	88	return fact
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	89
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	90	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	91	<p><a name="x_752"></a>An important point to note at this point is that, a function can return any Python value or a Python object, which also includes a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	92	<span class="emphasis"><em>Tuple</em></span>. A
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	93	<span class="emphasis"><em>Tuple</em></span> is just a collection of values and those values themselves can be of any other valid Python datatypes, including
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	94	<span class="emphasis"><em>Lists</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	95	<span class="emphasis"><em>Tuples</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	96	<span class="emphasis"><em>Dictionaries</em></span> among other things. So effectively, if a function can return a tuple, it can return any number of values through a tuple
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	97	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	98	<p><a name="x_753"></a>Let us write a small function to swap two values:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	99	<pre class="programlisting">def swap(a, b):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	100	return b, a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	101
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	102	c, d = swap(a, b)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	103
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	104	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	105	<p><a name="x_754"></a>Function scope --------------- The variables used inside the function are confined to the function's scope and doesn't pollute the variables of the same name outside the scope of the function. Also the arguments passed to the function are passed by-value if it is of basic Python data type:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	106	<pre class="programlisting">def cant_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	107	n = 10
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	108
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	109	n = 5
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	110	cant_change(n)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	111
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	112	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	113	<p><a name="x_755"></a>Upon running this code, what do you think would have happened to value of n which was assigned 5 before the function call? If you have already tried out that snippet on the interpreter you already know that the value of n is not changed. This is true of any immutable types of Python like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	114	<span class="emphasis"><em>Numbers</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	115	<span class="emphasis"><em>Strings</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	116	<span class="emphasis"><em>Tuples</em></span>. But when you pass mutable objects like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	117	<span class="emphasis"><em>Lists</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	118	<span class="emphasis"><em>Dictionaries</em></span> the values are manipulated even outside the function:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	119	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	120	<pre class="programlisting">>>> def can_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	121	... n[1] = James
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	122	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	123
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	124	>>> name = ['Mr.', 'Steve', 'Gosling']
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	125	>>> can_change(name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	126	>>> name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	127	['Mr.', 'James', 'Gosling']
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><a name="x_756"></a>If nothing is returned by the function explicitly, Python takes care to return None when the funnction is called.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	131	<div class="section" title="1. Default Arguments">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	132	<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	133	<a name="default-arguments"></a>1. Default Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	134	<p><a name="x_757"></a>There may be situations where we need to allow the functions to take the arguments optionally. Python allows us to define function this way by providing a facility called
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	135	<span class="emphasis"><em>Default Arguments</em></span>. For example, we need to write a function that returns a list of fibonacci numbers. Since our function cannot generate an infinite list of fibonacci numbers, we need to specify the number of elements that the fibonacci sequence must contain. Suppose, additionally, we want to the function to return 10 numbers in the sequence if no option is specified we can define the function as follows:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	136	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	137	<pre class="programlisting">def fib(n=10):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	138	fib_list = [0, 1]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	139	for i in range(n - 2):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	140	next = fib_list[-2] + fib_list[-1]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	141	fib_list.append(next)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	142	return fib_list
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	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	145	<p><a name="x_758"></a>When we call this function, we can optionally specify the value for the parameter n, during the call as an argument. Calling with no argument and argument with n=5 returns the following fibonacci sequences:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	146	<pre class="programlisting">fib()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	147	[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	148	fib(5)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	149	[0, 1, 1, 2, 3]
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	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	152	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	153	<div class="section" title="2. Keyword Arguments">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	154	<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	155	<a name="keyword-arguments"></a>2. Keyword Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	156	<p><a name="x_759"></a>When a function takes a large number of arguments, it may be difficult to remember the order of the parameters in the function definition or it may be necessary to pass values to only certain parameters since others take the default value. In either of these cases, Python provides the facility of passing arguments by specifying the name of the parameter as defined in the function definition. This is known as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	157	<span class="emphasis"><em>Keyword Arguments</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	158	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	159	<p><a name="x_75a"></a>In a function call,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	160	<span class="emphasis"><em>Keyword arguments</em></span> can be used for each argument, in the following fashion:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	161	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	162	<pre class="programlisting">argument_name=argument_value
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	163	Also denoted as: keyword=argument
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	def wish(name='World', greetings='Hello'):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	166	print "%s, %s!" % (greetings, name)
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><a name="x_75b"></a>This function can be called in one of the following ways. It is important to note that no restriction is imposed in the order in which
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	170	<span class="emphasis"><em>Keyword arguments</em></span> can be specified. Also note, that we have combined
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	171	<span class="emphasis"><em>Keyword arguments</em></span> with
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	172	<span class="emphasis"><em>Default arguments</em></span> in this example, however it is not necessary:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	173	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	174	<pre class="programlisting">wish(name='Guido', greetings='Hey')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	175	wish(greetings='Hey', name='Guido')
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	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	178	<p><a name="x_75c"></a>Calling functions by specifying arguments in the order of parameters specified in the function definition is called as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	179	<span class="emphasis"><em>Positional arguments</em></span>, as opposed to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	180	<span class="emphasis"><em>Keyword arguments</em></span>. It is possible to use both
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	181	<span class="emphasis"><em>Positional arguments</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	182	<span class="emphasis"><em>Keyword arguments</em></span> in a single function call. But Python doesn't allow us to bungle up both of them. The arguments to the function, in the call, must always start with
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	183	<span class="emphasis"><em>Positional arguments</em></span> which is in turn followed by
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	184	<span class="emphasis"><em>Keyword arguments</em></span>:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	185	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	186	<pre class="programlisting">def my_func(x, y, z, u, v, w):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	187	# initialize variables.
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	# do some stuff
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	190	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	191	# return the value
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	192
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	193	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	194	<p><a name="x_75d"></a>It is valid to call the above functions in the following ways:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	195	<pre class="programlisting">my_func(10, 20, 30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	196	my_func(10, 20, 30, 1.0, 2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	197	my_func(10, 20, z=30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	198	my_func(x=10, y=20, z=30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	199
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	200	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	201	<p><a name="x_75e"></a>Following lists some of the invalid calls:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	202	<pre class="programlisting">my_func(10, 20, z=30, 1.0, 2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	203	my_func(x=10, 20, z=30, 1.0, 2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	204	my_func(x=10, y=20, z=30, u=1.0, v=2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	205
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	206	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	207	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	208	<div class="section" title="3. Parameter Packing and Unpacking">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	209	<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	210	<a name="parameter-packing-and-unpacking"></a>3. Parameter Packing and Unpacking</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	211	<p><a name="x_75f"></a>The positional arguments passed to a function can be collected in a tuple parameter and keyword arguments can be collected in a dictionary. Since keyword arguments must always be the last set of arguments passed to a function, the keyword dictionary parameter must be the last parameter. The function definition must include a list explicit parameters, followed by tuple paramter collecting parameter, whose name is preceded by a ***, for collecting positional parameters, in turn followed by the dictionary collecting parameter, whose name is preceded by a **** :</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	212	<pre class="programlisting">def print_report(title, args, *name):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	213	"""Structure of args
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	214	(age, email-id)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	215	Structure of name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	216	{
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	217	'first': First Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	218	'middle': Middle Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	219	'last': Last Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	220	}
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	221	"""
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	222
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	223	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	224	print "Full name: %(first)s %(middle)s %(last)s" % name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	225	print "Age: %d\nEmail-ID: %s" % args
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	226
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	227	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	228	<p><a name="x_760"></a>The above function can be called as. Note, the order of keyword parameters can be interchanged:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	229	<pre class="programlisting">>>> print_report('Employee Report', 29, 'johny@example.com', first='Johny',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	230	last='Charles', middle='Douglas')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	231	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	232	Full name: Johny Douglas Charles
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	233	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	234	Email-ID: johny@example.com
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><a name="x_761"></a>The reverse of this can also be achieved by using a very identical syntax while calling the function. A tuple or a dictionary can be passed as arguments in place of a list of Positional arguments or Keyword arguments respectively using *** or **** :</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	238	<pre class="programlisting">def print_report(title, age, email, first, middle, last):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	239	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	240	print "Full name: %s %s %s" % (first, middle, last)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	241	print "Age: %d\nEmail-ID: %s" % (age, email)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	242
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	243	>>> args = (29, 'johny@example.com')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	244	>>> name = {
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	245	'first': 'Johny',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	246	'middle': 'Charles',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	247	'last': 'Douglas'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	248	}
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	249	>>> print_report('Employee Report', args, *name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	250	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	251	Full name: Johny Charles Douglas
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	252	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	253	Email-ID: johny@example.com
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	254
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	255	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	256	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	257	<div class="section" title="4. Nested Functions and Scopes">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	258	<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	259	<a name="nested-functions-and-scopes"></a>4. Nested Functions and Scopes</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	260	<p><a name="x_762"></a>Python allows nesting one function inside another. This style of programming turns out to be extremely flexible and powerful features when we use
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	261	<span class="emphasis"><em>Python decorators</em></span>. We will not talk about decorators is beyond the scope of this course. If you are interested in knowing more about
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	262	<span class="emphasis"><em>decorator programming</em></span> in Python you are suggested to read:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	263	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	264	<div class="literallayout"><p><br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	265	<a class="ulink" href="http://avinashv.net/2008/04/python-decorators-syntactic-sugar" target="_top">http://avinashv.net/2008/04/python-decorators-syntactic-sugar</a>/<br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	266	<a class="ulink" href="http://personalpages.tds.net" target="_top">http://personalpages.tds.net</a>/~kent37/kk/00001.html<br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	267	</p></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	268	<p><a name="x_763"></a>However, the following is an example for nested functions in Python:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	269	<pre class="programlisting">def outer():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	270	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	271	def inner():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	272	print "Inner..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	273	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	274	inner()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	275
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	276	>>> outer()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	277
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	278	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	279	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	280	<div class="section" title="5. map, reduce and filter functions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	281	<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	282	<a name="map-reduce-and-filter-functions"></a>5. map, reduce and filter functions</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	283	<p><a name="x_764"></a>Python provides several built-in functions for convenience. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	284	<span class="strong"><strong>map()</strong></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	285	<span class="strong"><strong>reduce()</strong></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	286	<span class="strong"><strong>filter()</strong></span> functions prove to be very useful with sequences like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	287	<span class="emphasis"><em>Lists</em></span>.
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><a name="x_765"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	290	<span class="strong"><strong>map</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	291	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	292	<span class="emphasis"><em>sequence</em></span>) function takes two arguments:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	293	<span class="emphasis"><em>function</em></span> and a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	294	<span class="emphasis"><em>sequence</em></span> argument. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	295	<span class="emphasis"><em>function</em></span> argument must be the name of the function which in turn takes a single argument, the individual element of the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	296	<span class="emphasis"><em>sequence</em></span>. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	297	<span class="strong"><strong>map</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	298	<span class="emphasis"><em>function(item)</em></span>, for each item in the sequence and returns a list of values, where each value is the value returned by each call to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	299	<span class="emphasis"><em>function(item)</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	300	<span class="strong"><strong>map()</strong></span> function allows to pass more than one sequence. In this case, the first argument,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	301	<span class="emphasis"><em>function</em></span> must take as many arguments as the number of sequences passed. This function is called with each corresponding element in the each of the sequences, or
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	302	<span class="strong"><strong>None</strong></span> if one of the sequence is exhausted:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	303	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	304	<pre class="programlisting">def square(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	305	return x*x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	306
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	307	>>> map(square, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	308	[1, 4, 9, 16]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	309
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	310	def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	311	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	312
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	313	>>> map(mul, [1, 2, 3, 4], [6, 7, 8, 9])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	314
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	315	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	316	<p><a name="x_766"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	317	<span class="strong"><strong>filter</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	318	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	319	<span class="emphasis"><em>sequence</em></span>) function takes two arguments, similar to the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	320	<span class="strong"><strong>map()</strong></span> function. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	321	<span class="strong"><strong>filter</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	322	<span class="emphasis"><em>function(item)</em></span>, for each item in the sequence and returns all the elements in the sequence for which
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	323	<span class="emphasis"><em>function(item)</em></span> returned True:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	324	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	325	<pre class="programlisting">def even(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	326	if x % 2:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	327	return True
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	328	else:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	329	return False
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	330
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	331	>>> filter(even, range(1, 10))
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	332	[1, 3, 5, 7, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	333
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	334	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	335	<p><a name="x_767"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	336	<span class="strong"><strong>reduce</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	337	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	338	<span class="emphasis"><em>sequence</em></span>) function takes two arguments, similar to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	339	<span class="strong"><strong>map</strong></span> function, however multiple sequences are not allowed. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	340	<span class="strong"><strong>reduce</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	341	<span class="emphasis"><em>function</em></span> with first two consecutive elements in the sequence, obtains the result, calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	342	<span class="emphasis"><em>function</em></span> with the result and the subsequent element in the sequence and so on until the end of the list and returns the final result:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	343	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	344	<pre class="programlisting">def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	345	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	346
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	347	>>> reduce(mul, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	348	24
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	349
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	350	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	351	<div class="section" title="5.1. List Comprehensions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	352	<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	353	<a name="list-comprehensions"></a>5.1. List Comprehensions</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	354	<p><a name="x_768"></a>List Comprehension is a convenvience utility provided by Python. It is a syntatic sugar to create
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	355	<span class="emphasis"><em>Lists</em></span>. Using
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	356	<span class="emphasis"><em>List Comprehensions</em></span> one can create
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	357	<span class="emphasis"><em>Lists</em></span> from other type of sequential data structures or other
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	358	<span class="emphasis"><em>Lists</em></span> itself. The syntax of
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	359	<span class="emphasis"><em>List Comprehensions</em></span> consists of a square brackets to indicate the result is a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	360	<span class="emphasis"><em>List</em></span> within which we include at least one
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	361	<span class="strong"><strong>for</strong></span> clause and multiple
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	362	<span class="strong"><strong>if</strong></span> clauses. It will be more clear with an example:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	363	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	364	<pre class="programlisting">>>> num = [1, 2, 3]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	365	>>> sq = [x*x for x in num]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	366	>>> sq
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	367	[1, 4, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	368	>>> all_num = [1, 2, 3, 4, 5, 6, 7, 8, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	369	>>> even = [x for x in all_num if x%2 == 0]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	370
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	371	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	372	<p><a name="x_769"></a>The syntax used here is very clear from the way it is written. It can be translated into english as, "for each element x in the list all_num, if remainder of x divided by 2 is 0, add x to the list."</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	373	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	374	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	375	</div></body>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	376	</html>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	377	<html>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	378	<head>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	379	<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	380	<title>Functional Approach</title>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	381	<link rel="stylesheet" href="hgbook.css" type="text/css">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	382	<meta name="generator" content="DocBook XSL Stylesheets V1.75.1">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	383	</head>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	384	<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="article" title="Functional Approach">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	385	<div class="titlepage">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	386	<div><div><h2 class="title">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	387	<a name="id2760558"></a>Functional Approach</h2></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	388	<hr>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	389	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	390	<div class="toc">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	391	<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	392	<dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	393	<dt><span class="section"><a href="#default-arguments">1. Default Arguments</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	394	<dt><span class="section"><a href="#keyword-arguments">2. Keyword Arguments</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	395	<dt><span class="section"><a href="#parameter-packing-and-unpacking">3. Parameter Packing and Unpacking</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	396	<dt><span class="section"><a href="#nested-functions-and-scopes">4. Nested Functions and Scopes</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	397	<dt><span class="section"><a href="#map-reduce-and-filter-functions">5. map, reduce and filter functions</a></span></dt>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	398	<dd><dl><dt><span class="section"><a href="#list-comprehensions">5.1. List Comprehensions</a></span></dt></dl></dd>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	399	</dl>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	400	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	401	<p><a name="x_74b"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	402	<span class="emphasis"><em>Functions</em></span> allow us to enclose a set of statements and call the function again and again instead of repeating the group of statements everytime. Functions also allow us to isolate a piece of code from all the other code and provides the convenience of not polluting the global variables.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	403	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	404	<p><a name="x_74c"></a>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	405	<span class="emphasis"><em>Function</em></span> in python is defined with the keyword
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	406	<span class="strong"><strong>def</strong></span> followed by the name of the function, in turn followed by a pair of parenthesis which encloses the list of parameters to the function. The definition line ends with a ':'. The definition line is followed by the body of the function intended by one block. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	407	<span class="emphasis"><em>Function</em></span> must return a value:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	408	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	409	<pre class="programlisting">def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	410	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	411	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	412	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	413
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	414	return fact
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	415
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	416	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	417	<p><a name="x_74d"></a>The code snippet above defines a function with the name factorial, takes the number for which the factorial must be computed, computes the factorial and returns the value.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	418	<p><a name="x_74e"></a>A
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	419	<span class="emphasis"><em>Function</em></span> once defined can be used or called anywhere else in the program. We call a fucntion with its name followed by a pair of parenthesis which encloses the arguments to the function.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	420	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	421	<p><a name="x_74f"></a>The value that function returns can be assigned to a variable. Let's call the above function and store the factorial in a variable:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	422	<pre class="programlisting">fact5 = factorial(5)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	423
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	424	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	425	<p><a name="x_750"></a>The value of fact5 will now be 120, which is the factorial of 5. Note that we passed 5 as the argument to the function.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	426	<p><a name="x_751"></a>It may be necessary to document what the function does, for each of the function to help the person who reads our code to understand it better. In order to do this Python allows the first line of the function body to be a string. This string is called as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	427	<span class="emphasis"><em>Documentation String</em></span> or
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	428	<span class="emphasis"><em>docstring</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	429	<span class="emphasis"><em>docstrings</em></span> prove to be very handy since there are number of tools which can pull out all the docstrings from Python functions and generate the documentation automatically from it.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	430	<span class="emphasis"><em>docstrings</em></span> for functions can be written as follows:
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">def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	433	'Returns the factorial for the number n.'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	434	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	435	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	436	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	437
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	438	return fact
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	439
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	440	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	441	<p><a name="x_752"></a>An important point to note at this point is that, a function can return any Python value or a Python object, which also includes a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	442	<span class="emphasis"><em>Tuple</em></span>. A
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	443	<span class="emphasis"><em>Tuple</em></span> is just a collection of values and those values themselves can be of any other valid Python datatypes, including
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	444	<span class="emphasis"><em>Lists</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	445	<span class="emphasis"><em>Tuples</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	446	<span class="emphasis"><em>Dictionaries</em></span> among other things. So effectively, if a function can return a tuple, it can return any number of values through a tuple
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	447	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	448	<p><a name="x_753"></a>Let us write a small function to swap two values:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	449	<pre class="programlisting">def swap(a, b):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	450	return b, a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	451
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	452	c, d = swap(a, b)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	453
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	454	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	455	<p><a name="x_754"></a>Function scope --------------- The variables used inside the function are confined to the function's scope and doesn't pollute the variables of the same name outside the scope of the function. Also the arguments passed to the function are passed by-value if it is of basic Python data type:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	456	<pre class="programlisting">def cant_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	457	n = 10
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	458
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	459	n = 5
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	460	cant_change(n)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	461
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	462	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	463	<p><a name="x_755"></a>Upon running this code, what do you think would have happened to value of n which was assigned 5 before the function call? If you have already tried out that snippet on the interpreter you already know that the value of n is not changed. This is true of any immutable types of Python like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	464	<span class="emphasis"><em>Numbers</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	465	<span class="emphasis"><em>Strings</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	466	<span class="emphasis"><em>Tuples</em></span>. But when you pass mutable objects like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	467	<span class="emphasis"><em>Lists</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	468	<span class="emphasis"><em>Dictionaries</em></span> the values are manipulated even outside the function:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	469	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	470	<pre class="programlisting">>>> def can_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	471	... n[1] = James
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
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	474	>>> name = ['Mr.', 'Steve', 'Gosling']
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	475	>>> can_change(name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	476	>>> name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	477	['Mr.', 'James', 'Gosling']
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	478
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	479	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	480	<p><a name="x_756"></a>If nothing is returned by the function explicitly, Python takes care to return None when the funnction is called.</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	481	<div class="section" title="1. Default Arguments">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	482	<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	483	<a name="default-arguments"></a>1. Default Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	484	<p><a name="x_757"></a>There may be situations where we need to allow the functions to take the arguments optionally. Python allows us to define function this way by providing a facility called
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	485	<span class="emphasis"><em>Default Arguments</em></span>. For example, we need to write a function that returns a list of fibonacci numbers. Since our function cannot generate an infinite list of fibonacci numbers, we need to specify the number of elements that the fibonacci sequence must contain. Suppose, additionally, we want to the function to return 10 numbers in the sequence if no option is specified we can define the function as follows:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	486	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	487	<pre class="programlisting">def fib(n=10):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	488	fib_list = [0, 1]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	489	for i in range(n - 2):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	490	next = fib_list[-2] + fib_list[-1]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	491	fib_list.append(next)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	492	return fib_list
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	493
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	494	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	495	<p><a name="x_758"></a>When we call this function, we can optionally specify the value for the parameter n, during the call as an argument. Calling with no argument and argument with n=5 returns the following fibonacci sequences:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	496	<pre class="programlisting">fib()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	497	[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	498	fib(5)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	499	[0, 1, 1, 2, 3]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	500
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	501	</pre>
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="2. Keyword Arguments">
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="keyword-arguments"></a>2. Keyword Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	506	<p><a name="x_759"></a>When a function takes a large number of arguments, it may be difficult to remember the order of the parameters in the function definition or it may be necessary to pass values to only certain parameters since others take the default value. In either of these cases, Python provides the facility of passing arguments by specifying the name of the parameter as defined in the function definition. This is known as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	507	<span class="emphasis"><em>Keyword Arguments</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	508	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	509	<p><a name="x_75a"></a>In a function call,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	510	<span class="emphasis"><em>Keyword arguments</em></span> can be used for each argument, in the following fashion:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	511	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	512	<pre class="programlisting">argument_name=argument_value
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	513	Also denoted as: keyword=argument
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	514
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	515	def wish(name='World', greetings='Hello'):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	516	print "%s, %s!" % (greetings, name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	517
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	518	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	519	<p><a name="x_75b"></a>This function can be called in one of the following ways. It is important to note that no restriction is imposed in the order in which
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	520	<span class="emphasis"><em>Keyword arguments</em></span> can be specified. Also note, that we have combined
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	521	<span class="emphasis"><em>Keyword arguments</em></span> with
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	522	<span class="emphasis"><em>Default arguments</em></span> in this example, however it is not necessary:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	523	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	524	<pre class="programlisting">wish(name='Guido', greetings='Hey')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	525	wish(greetings='Hey', name='Guido')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	526
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	527	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	528	<p><a name="x_75c"></a>Calling functions by specifying arguments in the order of parameters specified in the function definition is called as
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	529	<span class="emphasis"><em>Positional arguments</em></span>, as opposed to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	530	<span class="emphasis"><em>Keyword arguments</em></span>. It is possible to use both
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	531	<span class="emphasis"><em>Positional arguments</em></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	532	<span class="emphasis"><em>Keyword arguments</em></span> in a single function call. But Python doesn't allow us to bungle up both of them. The arguments to the function, in the call, must always start with
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	533	<span class="emphasis"><em>Positional arguments</em></span> which is in turn followed by
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	534	<span class="emphasis"><em>Keyword arguments</em></span>:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	535	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	536	<pre class="programlisting">def my_func(x, y, z, u, v, w):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	537	# initialize variables.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	538	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	539	# do some stuff
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	540	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	541	# return the value
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	542
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	543	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	544	<p><a name="x_75d"></a>It is valid to call the above functions in the following ways:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	545	<pre class="programlisting">my_func(10, 20, 30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	546	my_func(10, 20, 30, 1.0, 2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	547	my_func(10, 20, z=30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	548	my_func(x=10, y=20, z=30, u=1.0, v=2.0, w=3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	549
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	550	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	551	<p><a name="x_75e"></a>Following lists some of the invalid calls:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	552	<pre class="programlisting">my_func(10, 20, z=30, 1.0, 2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	553	my_func(x=10, 20, z=30, 1.0, 2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	554	my_func(x=10, y=20, z=30, u=1.0, v=2.0, 3.0)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	555
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	556	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	557	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	558	<div class="section" title="3. Parameter Packing and Unpacking">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	559	<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	560	<a name="parameter-packing-and-unpacking"></a>3. Parameter Packing and Unpacking</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	561	<p><a name="x_75f"></a>The positional arguments passed to a function can be collected in a tuple parameter and keyword arguments can be collected in a dictionary. Since keyword arguments must always be the last set of arguments passed to a function, the keyword dictionary parameter must be the last parameter. The function definition must include a list explicit parameters, followed by tuple paramter collecting parameter, whose name is preceded by a ***, for collecting positional parameters, in turn followed by the dictionary collecting parameter, whose name is preceded by a **** :</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	562	<pre class="programlisting">def print_report(title, args, *name):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	563	"""Structure of args
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	564	(age, email-id)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	565	Structure of name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	566	{
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	567	'first': First Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	568	'middle': Middle Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	569	'last': Last Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	570	}
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	571	"""
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	572
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	573	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	574	print "Full name: %(first)s %(middle)s %(last)s" % name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	575	print "Age: %d\nEmail-ID: %s" % args
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	576
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	577	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	578	<p><a name="x_760"></a>The above function can be called as. Note, the order of keyword parameters can be interchanged:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	579	<pre class="programlisting">>>> print_report('Employee Report', 29, 'johny@example.com', first='Johny',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	580	last='Charles', middle='Douglas')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	581	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	582	Full name: Johny Douglas Charles
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	583	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	584	Email-ID: johny@example.com
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	585
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	586	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	587	<p><a name="x_761"></a>The reverse of this can also be achieved by using a very identical syntax while calling the function. A tuple or a dictionary can be passed as arguments in place of a list of Positional arguments or Keyword arguments respectively using *** or **** :</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	588	<pre class="programlisting">def print_report(title, age, email, first, middle, last):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	589	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	590	print "Full name: %s %s %s" % (first, middle, last)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	591	print "Age: %d\nEmail-ID: %s" % (age, email)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	592
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	593	>>> args = (29, 'johny@example.com')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	594	>>> name = {
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	595	'first': 'Johny',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	596	'middle': 'Charles',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	597	'last': 'Douglas'
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	>>> print_report('Employee Report', args, *name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	600	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	601	Full name: Johny Charles Douglas
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	602	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	603	Email-ID: johny@example.com
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	604
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	605	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	606	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	607	<div class="section" title="4. Nested Functions and Scopes">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	608	<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	609	<a name="nested-functions-and-scopes"></a>4. Nested Functions and Scopes</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	610	<p><a name="x_762"></a>Python allows nesting one function inside another. This style of programming turns out to be extremely flexible and powerful features when we use
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	611	<span class="emphasis"><em>Python decorators</em></span>. We will not talk about decorators is beyond the scope of this course. If you are interested in knowing more about
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	612	<span class="emphasis"><em>decorator programming</em></span> in Python you are suggested to read:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	613	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	614	<div class="literallayout"><p><br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	615	<a class="ulink" href="http://avinashv.net/2008/04/python-decorators-syntactic-sugar" target="_top">http://avinashv.net/2008/04/python-decorators-syntactic-sugar</a>/<br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	616	<a class="ulink" href="http://personalpages.tds.net" target="_top">http://personalpages.tds.net</a>/~kent37/kk/00001.html<br>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	617	</p></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	618	<p><a name="x_763"></a>However, the following is an example for nested functions in Python:</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	619	<pre class="programlisting">def outer():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	620	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	621	def inner():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	622	print "Inner..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	623	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	624	inner()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	625
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	626	>>> outer()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	627
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	628	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	629	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	630	<div class="section" title="5. map, reduce and filter functions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	631	<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	632	<a name="map-reduce-and-filter-functions"></a>5. map, reduce and filter functions</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	633	<p><a name="x_764"></a>Python provides several built-in functions for convenience. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	634	<span class="strong"><strong>map()</strong></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	635	<span class="strong"><strong>reduce()</strong></span> and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	636	<span class="strong"><strong>filter()</strong></span> functions prove to be very useful with sequences like
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	637	<span class="emphasis"><em>Lists</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	638	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	639	<p><a name="x_765"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	640	<span class="strong"><strong>map</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	641	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	642	<span class="emphasis"><em>sequence</em></span>) function takes two arguments:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	643	<span class="emphasis"><em>function</em></span> and a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	644	<span class="emphasis"><em>sequence</em></span> argument. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	645	<span class="emphasis"><em>function</em></span> argument must be the name of the function which in turn takes a single argument, the individual element of the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	646	<span class="emphasis"><em>sequence</em></span>. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	647	<span class="strong"><strong>map</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	648	<span class="emphasis"><em>function(item)</em></span>, for each item in the sequence and returns a list of values, where each value is the value returned by each call to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	649	<span class="emphasis"><em>function(item)</em></span>.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	650	<span class="strong"><strong>map()</strong></span> function allows to pass more than one sequence. In this case, the first argument,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	651	<span class="emphasis"><em>function</em></span> must take as many arguments as the number of sequences passed. This function is called with each corresponding element in the each of the sequences, or
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	652	<span class="strong"><strong>None</strong></span> if one of the sequence is exhausted:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	653	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	654	<pre class="programlisting">def square(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	655	return x*x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	656
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	657	>>> map(square, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	658	[1, 4, 9, 16]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	659
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	660	def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	661	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	662
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	663	>>> map(mul, [1, 2, 3, 4], [6, 7, 8, 9])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	664
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	665	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	666	<p><a name="x_766"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	667	<span class="strong"><strong>filter</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	668	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	669	<span class="emphasis"><em>sequence</em></span>) function takes two arguments, similar to the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	670	<span class="strong"><strong>map()</strong></span> function. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	671	<span class="strong"><strong>filter</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	672	<span class="emphasis"><em>function(item)</em></span>, for each item in the sequence and returns all the elements in the sequence for which
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	673	<span class="emphasis"><em>function(item)</em></span> returned True:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	674	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	675	<pre class="programlisting">def even(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	676	if x % 2:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	677	return True
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	678	else:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	679	return False
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	680
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	681	>>> filter(even, range(1, 10))
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	682	[1, 3, 5, 7, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	683
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	684	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	685	<p><a name="x_767"></a>The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	686	<span class="strong"><strong>reduce</strong></span> (
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	687	<span class="emphasis"><em>function</em></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	688	<span class="emphasis"><em>sequence</em></span>) function takes two arguments, similar to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	689	<span class="strong"><strong>map</strong></span> function, however multiple sequences are not allowed. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	690	<span class="strong"><strong>reduce</strong></span> function calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	691	<span class="emphasis"><em>function</em></span> with first two consecutive elements in the sequence, obtains the result, calls
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	692	<span class="emphasis"><em>function</em></span> with the result and the subsequent element in the sequence and so on until the end of the list and returns the final result:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	693	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	694	<pre class="programlisting">def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	695	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	696
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	697	>>> reduce(mul, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	698	24
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	699
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	700	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	701	<div class="section" title="5.1. List Comprehensions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	702	<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	703	<a name="list-comprehensions"></a>5.1. List Comprehensions</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	704	<p><a name="x_768"></a>List Comprehension is a convenvience utility provided by Python. It is a syntatic sugar to create
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	705	<span class="emphasis"><em>Lists</em></span>. Using
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	706	<span class="emphasis"><em>List Comprehensions</em></span> one can create
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	707	<span class="emphasis"><em>Lists</em></span> from other type of sequential data structures or other
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	708	<span class="emphasis"><em>Lists</em></span> itself. The syntax of
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	709	<span class="emphasis"><em>List Comprehensions</em></span> consists of a square brackets to indicate the result is a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	710	<span class="emphasis"><em>List</em></span> within which we include at least one
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	711	<span class="strong"><strong>for</strong></span> clause and multiple
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	712	<span class="strong"><strong>if</strong></span> clauses. It will be more clear with an example:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	713	</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	714	<pre class="programlisting">>>> num = [1, 2, 3]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	715	>>> sq = [x*x for x in num]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	716	>>> sq
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	717	[1, 4, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	718	>>> all_num = [1, 2, 3, 4, 5, 6, 7, 8, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	719	>>> even = [x for x in all_num if x%2 == 0]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	720
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	721	</pre>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	722	<p><a name="x_769"></a>The syntax used here is very clear from the way it is written. It can be translated into english as, "for each element x in the list all_num, if remainder of x divided by 2 is 0, add x to the list."</p>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	723	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	724	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	725	</div></body>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	726	</html>

author	amit@thunder
	Mon, 25 Jan 2010 18:56:45 +0530
changeset 0	8083d21c0020
permissions	-rwxr-xr-x