A Short notes on Python Programming

Function Definitions

The general form of a function definition:

def function_name(parameters):

    body

• def: a keyword indicating a function definition
• function_name: the function name
• parameters:
• the parameter(s) of the function, 0 or more and are separated by a comma
• a parameter is a variable whose value will be supplied when the function is called
• body:
• 1 or more statements, often ending with a return statement

Example of a function definition:

def f(x):

    return x ** 2      

return statement

The general form of a return statement:

return expression

The rules for executing a return statement:

1.     Evaluate the expression. This produces a memory address.

2.     Pass back that memory address to the caller. Exit the function.

Function Calls

Function calls are expressions and the result can be stored in a variable.

The general form of a function call:

function_name(arguments)

The rules for executing a function call:

1. Evaluate the arguments to produce memory addresses.
2. Store those memory addresses in the corresponding parameters.
3. Execute the body of the function.

Example of a function definition and function calls:

>>> def area(base, height):

        return base * height / 2

>>> area(3, 4)

6.0

>>> result = area(10, 7.45)

>>> result

37.25

Saving your programs to ".py" files

We usually save our Python programs in ".py" files. A file can contain multiple function definitions and other statements. Before calling a function from a ".py" file in the shell in IDLE, you need to first execute Run -> Run Module, or else the shell will not recognize the function call.