A function is a section of the program or a block of code that is written once and can be executed whenever required in the program. A function is a block of self-contained statements which has a valid name, parameters list, and body. Functions make programming more functional and modular to perform modular tasks. Python provides several built-in functions to complete tasks and also allows a user to create new functions as well.

There are two types of functions:

Built-In Functions: copy(), len(), count() are the some built-in functions.
User-defined Functions: Functions which are defined by a user known as user-defined functions.
Example: A general syntax of user defined function is given below.

def function_name(parameters list):
#— statements—
return a_value