What is user defined function?

Special functions defined by the software developer to perform some pre-defined task by giving some name to a set of statements.

We can avoid the use of those statements again and again. 

User defined functions are used to create the reusable code.

Python provides def keyword to define a function.

Function may or may not  return some value. Python provides the return keyword to return some value.

Syntax 1

def functioname():
   statements

Syntax 2

def functionname(arguments):
    statements 

Syntax 3

def functionname(arguments):
    statements 
    return value

Example 1

Write the Python code having a function cube() that takes a number and prints the cube of that number

Problem: The current cube() function is not a reusable function.

Example 2

Create a function cube() that take a number and returns cube of that number.

Create another function volume() that takes radius of a sphere and returns volume of the sphere by using the cube() function