User Defined Functions

In all programming and scripting language, a function is a block of program statements which can be used repetitively in a program. It saves the time of a developer. In Python concept of function is same as in other languages. There are some built-in functions which are part of Python. Besides that, we can define functions according to our need.

In Python, a user-defined function’s declaration begins with the keyword def and followed by the function name. The function may take arguments(s) as input within the opening and closing parentheses, just after the function name followed by a colon. After defining the function name and arguments(s) a block of program statement(s) start at the next line and these statement(s) must be indented. Here is the syntax of a user defined function.

Syntax

def function_name(argument1, argument2, ...) :
    statement_1 
    statement_2
    ....

Call a function

Calling a function in Python is similar to other programming languages, using the function name, parenthesis (opening and closing) and parameter(s). See the syntax, followed by an example.

Syntax

function_name(arg1, arg2)

Example :

def avg_number(x, y):  
    print("Average of ",x," and ",y, " is ",(x+y)/2)  
avg_number(3, 4)  

Output :

Average of 3 and 4 is 3.5

Explanation :

1. Lines 1-2 : Details (definition) of the function.
2. Line 3 : Call the function.
3. Line 1 : Pass parameters : x = 3, y = 4
4. Line 2 : Print the value of two parameters as well as their average value.

Function without arguments :

The following function has no arguments.

def function_name() :
    statement_1 
    statement_2
    ....

Example :

def printt():  
    print("I Love CodeCell")  
    print("I Love CodeCell")  
    print("I Love CodeCell")  
printt()  

Output :

I Love CodeCell
I Love CodeCell
I Love CodeCell

Explanation :

1. Lines 1-4 : Details (definition) of the function.
2. Line 5 : Call the function.
3. Line 1 : No parameter passes.
4. Line 2-4 : Execute three print statements.

The Return statement in function

In Python the return statement (the word return followed by an expression.) is used to return a value from a function, return statement without an expression argument returns none. See the syntax.

def function_name(argument1, argument2, ...) :
    statement_1 
    statement_2
    ....
    return expression

function_name(arg1, arg2)

Example :

The following function returns the square of the sum of two numbers.

def nsquare(x, y):  
    return (x*x + 2*x*y + y*y)  
print("The square of the sum of 2 and 3 is : ", nsquare(2, 3))  

Output :

The square of the sum of 2 and 3 is : 25

Explanation :

1. Lines 1-2 : Details (definition) of the function.
2. Line 3 : Call the function within a print statement.
3. Line 1 : Pass the parameters x = 2, y = 3
4. Line 2 : Calculate and return the value of (x + y)