Python functions

In Python, functions provide organized blocks of reusable code. Typically, this allows a programmer to write a block of code to perform a single, related action. While Python provides many built-in functions, a programmer can create user-defined functions. In addition to helping us to program and debug by dividing the program into parts, the functions also allow us to reuse code.

Python functions are defined using the def keyword with the function name, followed by the function parameters. The body of the function consists of Python statements that are to be executed. At the end of the function, you can choose to return a value to the function caller, or by default, it will return the None object if you do not specify a return value.

For example, we can define a function that, given a sequence of numbers and an item passed by a parameter, returns True if the element is within the sequence and False otherwise:

>>> def contains(sequence,item):
        for element in sequence:
                if element == item:
                        return True
        return False
>>> print contains([100,200,300,400],200)

True

>>> print contains([100,200,300,400],300)

True

>>> print contains([100,200,300,400],350)

False