Function in Python

 Function

         A function is a block of organised, reusable code that is used to perform a single, related action.

A functions is a set of statements that take input, do some specific computation and produce output. The idea is to put some commonly or repeatedly done task together and make a function. so that instead of writing the same code again and again for different inputs we can call the function.

Python allows us to divide a large program into the basic building blocks known as a function. 

Python provide us various inbuilt functions like range() or print(). Although, the user can create its functions, which can be called user-defined functions.

There are mainly two types of functions.

• User-define functions - The user-defined functions are those define by the user to perform the specific task.
• Built-in functions - The built-in functions are those functions that are pre-defined in Python.

Advantages of Function

There are the following advantages of Python functions.

• Using functions, we can avoid rewriting the same logic/code again and again in a program.
• We can call Python functions multiple times in a program and anywhere in a program.
• They break the large complex problem into small parts.
• Reusability is the main achievement of Python functions.
• They reduce duplication of code in a program.

Creating a function 

    Python provides a def keyword to define the function.

Here are simple rules to define a function in Python.

• Function block begin with the keyword def followed by the function name and parentheses ( ).

• Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses.

• The first statement of a function can be optional statement. This is called Documentation string of the function or Docstring.

• The code block within every function starts with a colon ( : ) and is indented.

• The return statement is used to return the value. A function can have only one return.

Syntax for Function Definition

def functionname(parameters):

            

            "function Docstring"               # optional

             statement(s)

             return(expression)

Function calling

  Defining a function only gives it a name, specifies the parameters that are to be included in the function and structure the block of code. Once the basic structure of a function is finalised, then you can execute it by calling it from another function or directly.

A function must be defined before the function call; otherwise, the Python interpreter gives an error. To call the function, use the function name followed by the parentheses.

Example

1. #function definition  
2. def hello_world():    
3.     print("hello world")    
4. # function calling  
5. hello_world()      

Output

hello world

Example

def printme(str):

        "this prints a passed string into this function"

         print(str)

         return

printme("i am first called to user defined function")

printme("again second call to the same function")

Output

i am first called to user defined function

again second call to the same function

Example 

1. # Defining function  
2. def sum():  
3.     a = 10  
4.     b = 20  
5.     c = a+b  
6.     return c  
7. # calling sum() function in print statement  
8. print("The sum is:",sum())  

Output

The sum is: 30

Example : Creating function without return statement

1. # Defining function  
2. def sum():  
3.     a = 10  
4.     b = 20  
5.     c = a+b  
6. # calling sum() function in print statement  
7. print(sum())  

Output

None