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8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	8	<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><span style="color: red"><html><span style="color: red"><body><span style="color: red"><document><span style="color: red"><title>Functional Approach</title></span><span style="color: red"><paragraph><span class="emphasis"><em>Functions</em></span> allow us to enclose a set of statements and call the function again
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	9	and again instead of repeating the group of statements everytime. Functions also
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	10	allow us to isolate a piece of code from all the other code and provides the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	11	convenience of not polluting the global variables.</paragraph></span><span style="color: red"><paragraph><span class="emphasis"><em>Function</em></span> in python is defined with the keyword <span style="color: red"><strong>def</strong></span> followed by the name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	12	of the function, in turn followed by a pair of parenthesis which encloses the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	13	list of parameters to the function. The definition line ends with a ':'. The
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	14	definition line is followed by the body of the function intended by one block.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	15	The <span class="emphasis"><em>Function</em></span> must return a value:</paragraph></span><span style="color: red"><literal_block>def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	16	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	17	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	18	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	19
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	20	return fact</literal_block></span><span style="color: red"><paragraph>The code snippet above defines a function with the name factorial, takes the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	21	number for which the factorial must be computed, computes the factorial and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	22	returns the value.</paragraph></span><span style="color: red"><paragraph>A <span class="emphasis"><em>Function</em></span> once defined can be used or called anywhere else in the program. We
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	23	call a fucntion with its name followed by a pair of parenthesis which encloses
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	24	the arguments to the function.</paragraph></span><span style="color: red"><paragraph>The value that function returns can be assigned to a variable. Let's call the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	25	above function and store the factorial in a variable:</paragraph></span><span style="color: red"><literal_block>fact5 = factorial(5)</literal_block></span><span style="color: red"><paragraph>The value of fact5 will now be 120, which is the factorial of 5. Note that we
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	26	passed 5 as the argument to the function.</paragraph></span><span style="color: red"><paragraph>It may be necessary to document what the function does, for each of the function
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	27	to help the person who reads our code to understand it better. In order to do
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	28	this Python allows the first line of the function body to be a string. This
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	29	string is called as <span class="emphasis"><em>Documentation String</em></span> or <span class="emphasis"><em>docstring</em></span>. <span class="emphasis"><em>docstrings</em></span> prove
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	30	to be very handy since there are number of tools which can pull out all the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	31	docstrings from Python functions and generate the documentation automatically
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	32	from it. <span class="emphasis"><em>docstrings</em></span> for functions can be written as follows:</paragraph></span><span style="color: red"><literal_block>def factorial(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	33	'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	34	fact = 1
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	35	for i in range(2, n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	36	fact *= i
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	37
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	38	return fact</literal_block></span><span style="color: red"><paragraph>An important point to note at this point is that, a function can return any
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	39	Python value or a Python object, which also includes a <span class="emphasis"><em>Tuple</em></span>. A <span class="emphasis"><em>Tuple</em></span> is
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	40	just a collection of values and those values themselves can be of any other
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	41	valid Python datatypes, including <span class="emphasis"><em>Lists</em></span>, <span class="emphasis"><em>Tuples</em></span>, <span class="emphasis"><em>Dictionaries</em></span> among other
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	42	things. So effectively, if a function can return a tuple, it can return any
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	43	number of values through a tuple</paragraph></span><span style="color: red"><paragraph>Let us write a small function to swap two values:</paragraph></span><span style="color: red"><literal_block>def swap(a, b):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	44	return b, a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	45
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	46	c, d = swap(a, b)</literal_block></span><div class="section" title="1. Function scope">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	47	<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	48	<a name="id2981898"></a>1. Function scope</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	49	<span style="color: red"><paragraph>The variables used inside the function are confined to the function's scope
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	50	and doesn't pollute the variables of the same name outside the scope of the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	51	function. Also the arguments passed to the function are passed by-value if
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	52	it is of basic Python data type:</paragraph></span><span style="color: red"><literal_block>def cant_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	53	n = 10
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	54
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	55	n = 5
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	56	cant_change(n)</literal_block></span><span style="color: red"><paragraph>Upon running this code, what do you think would have happened to value of n
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	57	which was assigned 5 before the function call? If you have already tried out
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	58	that snippet on the interpreter you already know that the value of n is not
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	59	changed. This is true of any immutable types of Python like <span class="emphasis"><em>Numbers</em></span>, <span class="emphasis"><em>Strings</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	60	and <span class="emphasis"><em>Tuples</em></span>. But when you pass mutable objects like <span class="emphasis"><em>Lists</em></span> and <span class="emphasis"><em>Dictionaries</em></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	61	the values are manipulated even outside the function:</paragraph></span><span style="color: red"><literal_block>>>> def can_change(n):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	62	... n[1] = James
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
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	65	>>> name = ['Mr.', 'Steve', 'Gosling']
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	66	>>> can_change(name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	67	>>> name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	68	['Mr.', 'James', 'Gosling']</literal_block></span><span style="color: red"><paragraph>If nothing is returned by the function explicitly, Python takes care to return
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	69	None when the funnction is called.</paragraph></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	70	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	71	<div class="section" title="2. Default Arguments">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	72	<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	73	<a name="id2981970"></a>2. Default Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	74	<span style="color: red"><paragraph>There may be situations where we need to allow the functions to take the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	75	arguments optionally. Python allows us to define function this way by providing
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	76	a facility called <span class="emphasis"><em>Default Arguments</em></span>. For example, we need to write a function
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	77	that returns a list of fibonacci numbers. Since our function cannot generate an
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	78	infinite list of fibonacci numbers, we need to specify the number of elements
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	79	that the fibonacci sequence must contain. Suppose, additionally, we want to the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	80	function to return 10 numbers in the sequence if no option is specified we can
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	81	define the function as follows:</paragraph></span><span style="color: red"><literal_block>def fib(n=10):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	82	fib_list = [0, 1]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	83	for i in range(n - 2):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	84	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	85	fib_list.append(next)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	86	return fib_list</literal_block></span><span style="color: red"><paragraph>When we call this function, we can optionally specify the value for the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	87	parameter n, during the call as an argument. Calling with no argument and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	88	argument with n=5 returns the following fibonacci sequences:</paragraph></span><span style="color: red"><literal_block>fib()
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	89	[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	90	fib(5)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	91	[0, 1, 1, 2, 3]</literal_block></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	92	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	93	<div class="section" title="3. Keyword Arguments">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	94	<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	95	<a name="id2981995"></a>3. Keyword Arguments</h2></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	96	<span style="color: red"><paragraph>When a function takes a large number of arguments, it may be difficult to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	97	remember the order of the parameters in the function definition or it may
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	98	be necessary to pass values to only certain parameters since others take
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	99	the default value. In either of these cases, Python provides the facility
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	100	of passing arguments by specifying the name of the parameter as defined in
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	101	the function definition. This is known as <span class="emphasis"><em>Keyword Arguments</em></span>.</paragraph></span><span style="color: red"><paragraph>In a function call, <span class="emphasis"><em>Keyword arguments</em></span> can be used for each argument, in the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	102	following fashion:</paragraph></span><span style="color: red"><literal_block>argument_name=argument_value
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	103	Also denoted as: keyword=argument
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	104
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	105	def wish(name='World', greetings='Hello'):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	106	print "%s, %s!" % (greetings, name)</literal_block></span><span style="color: red"><paragraph>This function can be called in one of the following ways. It is important to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	107	note that no restriction is imposed in the order in which <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	108	can be specified. Also note, that we have combined <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	109	<span class="emphasis"><em>Default arguments</em></span> in this example, however it is not necessary:</paragraph></span><span style="color: red"><literal_block>wish(name='Guido', greetings='Hey')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	110	wish(greetings='Hey', name='Guido')</literal_block></span><span style="color: red"><paragraph>Calling functions by specifying arguments in the order of parameters specified
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	111	in the function definition is called as <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	112	<span class="emphasis"><em>Keyword arguments</em></span>. It is possible to use both <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	113	<span class="emphasis"><em>Keyword arguments</em></span> in a single function call. But Python doesn't allow us to
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	114	bungle up both of them. The arguments to the function, in the call, must always
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	115	start with <span class="emphasis"><em>Positional arguments</em></span> which is in turn followed by <span class="emphasis"><em>Keyword
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	116	arguments</em></span>:</paragraph></span><span style="color: red"><literal_block>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	117	# initialize variables.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	118	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	119	# do some stuff
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	120	...
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	121	# return the value</literal_block></span><span style="color: red"><paragraph>It is valid to call the above functions in the following ways:</paragraph></span><span style="color: red"><literal_block>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	122	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	123	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	124	my_func(x=10, y=20, z=30, u=1.0, v=2.0, w=3.0)</literal_block></span><span style="color: red"><paragraph>Following lists some of the invalid calls:</paragraph></span><span style="color: red"><literal_block>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	125	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	126	my_func(x=10, y=20, z=30, u=1.0, v=2.0, 3.0)</literal_block></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	127	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	128	<div class="section" title="4. Parameter Packing and Unpacking">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	129	<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	130	<a name="id2982116"></a>4. 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	131	<span style="color: red"><paragraph>The positional arguments passed to a function can be collected in a tuple
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	132	parameter and keyword arguments can be collected in a dictionary. Since keyword
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	133	arguments must always be the last set of arguments passed to a function, the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	134	keyword dictionary parameter must be the last parameter. The function definition
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	135	must include a list explicit parameters, followed by tuple paramter collecting
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	136	parameter, whose name is preceded by a <span style="color: red"><strong>*</strong></span>, for collecting positional
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	137	parameters, in turn followed by the dictionary collecting parameter, whose name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	138	is preceded by a <span style="color: red"><strong>*</strong></span></paragraph></span><span style="color: red"><literal_block>def print_report(title, args, **name):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	139	"""Structure of args
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	140	(age, email-id)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	141	Structure of name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	142	{
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	143	'first': First Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	144	'middle': Middle Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	145	'last': Last Name
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	146	}
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	147	"""
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	148
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	149	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	150	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	151	print "Age: %d\nEmail-ID: %s" % args</literal_block></span><span style="color: red"><paragraph>The above function can be called as. Note, the order of keyword parameters can
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	152	be interchanged:</paragraph></span><span style="color: red"><literal_block>>>> 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	153	last='Charles', middle='Douglas')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	154	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	155	Full name: Johny Douglas Charles
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	156	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	157	Email-ID: johny@example.com</literal_block></span><span style="color: red"><paragraph>The reverse of this can also be achieved by using a very identical syntax while
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	158	calling the function. A tuple or a dictionary can be passed as arguments in
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	159	place of a list of <span class="emphasis"><em>Positional arguments</em></span> or <span class="emphasis"><em>Keyword arguments</em></span> respectively
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	160	using <span style="color: red"><strong></strong></span> or <span style="color: red"><strong>*</strong></span></paragraph></span><span style="color: red"><literal_block>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	161	print "Title: %s" % (title)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	162	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	163	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	164
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	165	>>> args = (29, 'johny@example.com')
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	166	>>> name = {
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	167	'first': 'Johny',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	168	'middle': 'Charles',
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	169	'last': 'Douglas'
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	170	}
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	171	>>> print_report('Employee Report', args, *name)
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	172	Title: Employee Report
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	173	Full name: Johny Charles Douglas
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	174	Age: 29
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	175	Email-ID: johny@example.com</literal_block></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	176	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	177	<div class="section" title="5. Nested Functions and Scopes">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	178	<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	179	<a name="id2982188"></a>5. 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	180	<span style="color: red"><paragraph>Python allows nesting one function inside another. This style of programming
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	181	turns out to be extremely flexible and powerful features when we use <span class="emphasis"><em>Python
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	182	decorators</em></span>. We will not talk about decorators is beyond the scope of this
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	183	course. If you are interested in knowing more about <span class="emphasis"><em>decorator programming</em></span> in
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	184	Python you are suggested to read:</paragraph></span><span style="color: red"><line_block><span style="color: red"><line><div class="reference">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	185	<div class="titlepage"><hr></div>http://avinashv.net/2008/04/python-decorators-syntactic-sugar/</div></line></span><span style="color: red"><line><div class="reference">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	186	<div class="titlepage"><hr></div>http://personalpages.tds.net/~kent37/kk/00001.html</div></line></span></line_block></span><span style="color: red"><paragraph>However, the following is an example for nested functions in Python:</paragraph></span><span style="color: red"><literal_block>def outer():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	187	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	188	def inner():
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	189	print "Inner..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	190	print "Outer..."
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	191	inner()
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	>>> outer()</literal_block></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	194	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	195	<div class="section" title="6. map, reduce and filter functions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	196	<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	197	<a name="id2982258"></a>6. 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	198	<span style="color: red"><paragraph>Python provides several built-in functions for convenience. The <span style="color: red"><strong>map()</strong></span>,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	199	<span style="color: red"><strong>reduce()</strong></span> and <span style="color: red"><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	200	<span class="emphasis"><em>Lists</em></span>.</paragraph></span><span style="color: red"><paragraph>The <span style="color: red"><strong>map</strong></span> (<span class="emphasis"><em>function</em></span>, <span class="emphasis"><em>sequence</em></span>) function takes two arguments: <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	201	and a <span class="emphasis"><em>sequence</em></span> argument. The <span class="emphasis"><em>function</em></span> argument must be the name of the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	202	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	203	<span class="emphasis"><em>sequence</em></span>. The <span style="color: red"><strong>map</strong></span> function calls <span class="emphasis"><em>function(item)</em></span>, for each item in the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	204	sequence and returns a list of values, where each value is the value returned
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	205	by each call to <span class="emphasis"><em>function(item)</em></span>. <span style="color: red"><strong>map()</strong></span> function allows to pass more than
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	206	one sequence. In this case, the first argument, <span class="emphasis"><em>function</em></span> must take as many
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	207	arguments as the number of sequences passed. This function is called with each
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	208	corresponding element in the each of the sequences, or <span style="color: red"><strong>None</strong></span> if one of the
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	209	sequence is exhausted:</paragraph></span><span style="color: red"><literal_block>def square(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	210	return x*x
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	211
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	212	>>> map(square, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	213	[1, 4, 9, 16]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	214
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	215	def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	216	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	217
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	218	>>> map(mul, [1, 2, 3, 4], [6, 7, 8, 9])</literal_block></span><span style="color: red"><paragraph>The <span style="color: red"><strong>filter</strong></span> (<span class="emphasis"><em>function</em></span>, <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	219	the <span style="color: red"><strong>map()</strong></span> function. The <span style="color: red"><strong>filter</strong></span> function calls <span class="emphasis"><em>function(item)</em></span>, for each
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	220	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	221	<span class="emphasis"><em>function(item)</em></span> returned True:</paragraph></span><span style="color: red"><literal_block>def even(x):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	222	if x % 2:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	223	return True
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	224	else:
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	225	return False
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	>>> filter(even, range(1, 10))
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	228	[1, 3, 5, 7, 9]</literal_block></span><span style="color: red"><paragraph>The <span style="color: red"><strong>reduce</strong></span> (<span class="emphasis"><em>function</em></span>, <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	229	<span style="color: red"><strong>map</strong></span> function, however multiple sequences are not allowed. The <span style="color: red"><strong>reduce</strong></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	230	function calls <span class="emphasis"><em>function</em></span> with first two consecutive elements in the sequence,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	231	obtains the result, calls <span class="emphasis"><em>function</em></span> with the result and the subsequent element
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	232	in the sequence and so on until the end of the list and returns the final result:</paragraph></span><span style="color: red"><literal_block>def mul(x, y):
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	233	return x*y
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	234
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	235	>>> reduce(mul, [1, 2, 3, 4])
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	236	24</literal_block></span><div class="section" title="6.1. List Comprehensions">
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	237	<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	238	<a name="id2982429"></a>6.1. List Comprehensions</h3></div></div></div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	239	<span style="color: red"><paragraph>List Comprehension is a convenvience utility provided by Python. It is a
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	240	syntatic sugar to create <span class="emphasis"><em>Lists</em></span>. Using <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	241	<span class="emphasis"><em>Lists</em></span> from other type of sequential data structures or other <span class="emphasis"><em>Lists</em></span> itself.
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	242	The syntax of <span class="emphasis"><em>List Comprehensions</em></span> consists of a square brackets to indicate
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	243	the result is a <span class="emphasis"><em>List</em></span> within which we include at least one <span style="color: red"><strong>for</strong></span> clause and
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	244	multiple <span style="color: red"><strong>if</strong></span> clauses. It will be more clear with an example:</paragraph></span><span style="color: red"><literal_block>>>> num = [1, 2, 3]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	245	>>> 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	246	>>> sq
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	247	[1, 4, 9]
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	248	>>> 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	249	>>> even = [x for x in all_num if x%2 == 0]</literal_block></span><span style="color: red"><paragraph>The syntax used here is very clear from the way it is written. It can be
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	250	translated into english as, "for each element x in the list all_num,
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	251	if remainder of x divided by 2 is 0, add x to the list."</paragraph></span>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	252	</div>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	253	</div></document></span></body></span></html></span></body>
8083d21c0020 The first commit of all the required files for the review app amit@thunder parents: diff changeset	254	</html>

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