1 * Functions

     2 *** Outline

     3 ***** Functions

     4 ******* review of what's been done in solving equations tutorial

     5 ********* def

     6 ********* name

     7 ********* arguments

     8 ********* indented block

     9 ********* calling a function

    10 ******* arguments are local to a function

    11 ******* return values

    12 ******* doc strings - with example.

    13 ******* code reading exercises?

    14 ******* default arguments

    15 ******* keyword arguments

    16 ******* availability library functions

    17 *** Script

    18     Welcome friends. 

    19 

    20     In this tutorial we shall be looking at Functions. We already have

    21     looked at the basics of functions in the tutorial on solving

    22     equations. We shall first review these basics. Next we shall look

    23     at other details like doc-strings, default arguments and keyword

    24     arguments. 

    25 

    26     Let's write a simple function that prints a Hello message, after

    27     accepting a name. 

    28 

    29         def welcome(name):

    30 	    print "Hello", name 

    31 

    32     You would recall that def is a keyword that indicates a function

    33     definition. 'welcome' is the name of the function and 'name' is

    34     the lone argument to the function. Note that the function is

    35     defined within an indented block, similar to any other block. Our

    36     function welcome just has one line in it's definition.  

    37     

    38     We can call our function by passing, as follows -

    39         welcome("World")

    40 

    41     (arguments are local to a function)

    42 

    43     In general functions should be accompanied by documentation on how

    44     to use it. Python provides a convenient way of writing within the

    45     function itself, using doc strings. They were mentioned in the

    46     tutorial on strings. Let's look at how to write them here. 

    47 

    48     Let us add a simple doc string to our welcome function. 

    49 

    50         def welcome(name):

    51 	    """ Prints a hello message to a person, given a name. """

    52 	    print "Hello", name 

    53     

    54     Notice that the doc string uses triple quotes. If the doc-string

    55     exceeded one line, we could have used new line characters in

    56     it. Also, as expected the doc-string is indented as is required

    57     for anything within a block. 

    58 

    59     We shall now look at default arguments. 

    60     [show slide with examples of functions with default arguments]

    61     The strip function has been used in two different ways in the

    62     previous tutorials - one for splitting on spaces and the other for

    63     splitting on commas. 

    64 

    65     The function split is being called with no arguments and one

    66     argument, respectively. In the first case, white space is being

    67     used as a default value. Let's now edit our function, welcome, to

    68     use default values. (For convenience, we have dropped the doc-string)

    69 

    70         def welcome(name="World!"):

    71 	    print "Hello", name 

    72     

    73     Now, we call the function 'welcome' without passing any arguments

    74     to it. 

    75         welcome()

    76 

    77     "World!" is used as a default argument, when no name argument is

    78     passed to 'welcome'. 

    79 

    80     Let's now look at the use of keyword arguments. 

    81     [show slide with examples of functions with keyword arguments]

    82     We have already looked at functions and keyword arguments in these

    83     examples. loc, linewidth, xy, labels are all keywords. 

    84 

    85     Let's now see, how we can call our function 'welcome', using

    86     keyword arguments. We can call the function in a variety of ways.

    87         welcome("Hello", "James")

    88 	welcome("Hi", name="Guido")

    89 	welcome(name="Guido", greet="Hello")

    90 

    91     Keyword arguments allow us to call functions by passing arguments

    92     in any order and removes need to remember the order of arguments

    93     in the function definition. 

    94 

    95 

    96 ***** return values

    97 ***** arguments are local to a function

    98 ***** availability library functions

    99 ***** code reading exercises?

   100   

   101     We come to the end of this tutorial on functions. In this tutorial

   102     we have learnt about functions in a greater detail. We looked at

   103     how to define functions, calling them, default and keyword

   104     arguments. 

   105 

   106 *** Notes