USER-DEFINED FUNCTIONS IN PYTHON

Python provides built-in functions and also enables you to define your own functions. You can define functions to provide the required functionality. Here are simple rules to define a function in Python:

• Function blocks begin with the keyword def followed by the function name and parentheses.
• Any input arguments should be placed within these parentheses.
• The first statement of a function can be an optional statement—the documentation string of the function or docstring.
• The code block within every function starts with a colon (:) and is indented.
• The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.
• If a function does not specify return statement, the function automatically returns None, which is a special type of value in Python.

A very simple custom Python function is here:

>>> def func():
...   print 3
... 
>>> func()
3

The preceding function is trivial, but it does illustrate the syntax for defining custom functions in Python. The following example is slightly more useful:

>>> def func(x):
...   for i in range(0,x):
...     print(i)
... 
>>> func(5)
0
1
2
3
4