Class 12: User-Defined Python Functions

By: Archana Shukla and Rajesh Shukla

A User-defined Python function is a group of related statements that helps us to perform a specific task.

• The use of functions improves the clarity and readability of the program.
• It helps to break our program into smaller and modular chunks.
• As our program grows larger and larger, functions make it more organized and manageable. 
• The function makes them more efficient by reducing duplication of code.
• It breaks the complex tasks into more manageable parts.

Functions are also known as methods, modules, procedures, routines, sub-routines, or sub-program.

How to define a function

A user-defined python function is created using the keyword “def”. 

Syntax of Function    

#function definition
def function_name(list_of_parameters):
     """ docstring """
     statements
     statements
     statements
     return variable

A function definition in python consists of the following components.

def

• The keyword “def” marks the start of the function header.

function_name

• A function name helps us to identify the function.
• The function name should follow the rules of writing identifiers in Python.

List_of_parameters

• These help us to pass values to a function.
• These are optional.

colon (:)

• This marks the end of the function header.

docstring

• Optional documentation string (docstring) to describe the purpose/objective of the function.
• documentation is a good programming practice.

statements

• One or more valid python statements that make up the function body.
  Statements must have the same indentation level.

return variable

• An optional return statement to return a value from the function.

Example:

def hello():
      """ this is function named hello """
      print("we are in hello function")
def hi():
      ''' this is function hi
        to test function '''
      print("this is good function")
 
#function calling
print("to call a function ")
hello() #calling function hello()
hi() #calling function hi()
print() #just to leave blank line
print("printing doc string")
print(hello.__doc__) #to display doc string of function hello
print(hi.__doc__)  #to display doc string of function hello 

Output:

to call a function
we are in hello function
this is good function

printing doc string
this is function named hello
this is function hi
to test function
>>>

User-defined functions can further be divided into the following types:

* Functions without arguments
* Functions with arguments without returning any value
* function with arguments and returning value
* In Python a function can return multiple values(Very Important)