Function in Python

It is a collection of statement that performs an specific task.
It executes when it is called by its name.
A large program is divided into a number of small building block for simplicity and this building block is called function.
We can call a function again and again.
The most important features of function is code reusability.
def keyword is used to define function in python.

Syntax of function

def fun_name(parameter list):
  function_body

def

It is a keyword which is used to define function.

fun_name

It is the actual name of the function.
It is also used at the time of calling the function.

Parameter List

It is the place where we can pass a number of parameter/variable.
These variables may be used in the program.
The value of parameter is passed from the calling of function.
It is optional part.

Body

It is the place where the actual code is written to perform the specific task.

Example


#Function definition
def add():
    x=10
    y=30;
    z=x+y
    print("Add=",z)
#function calling
add()
"""
***Output***
Add=40
"""

Here add is function name.

Function with parameter


#Function definition
def fruits(name):
    print("I like ",name)
#function calling
fruits("Mango")
fruits("Orange")
fruits("Apple")
"""
***Output***
I like  Mango
I like  Orange
I like  Apple
"""


#Function definition
def fruits(name,fruit):
    print(name ," likes ",fruit)
#function calling
fruits("Anjali","Mango")
fruits("Nisha","Orange")
fruits("Rocky","Apple")
"""
***Output***
Anjali  likes  Mango
Nisha  likes  Orange
Rocky  likes  Apple
"""

Function with default parameter value

We can also assign a default value to a parameter.
If the function is called without argument, it uses the default value.


#Function definition
def fruits(name="Rocky",fruit="Apple"):
    print(name ," likes ",fruit)
#function calling without argument
fruits()
#function calling with argument
fruits("Nisha","Orange")
"""
***Output***
Rocky  likes  Apple
Nisha  likes  Orange
"""

Function with return type

We can also return a value from the function using return type.
return keyword is used to return a value.


#Function definition
def add(x,y):
    return (x+y)
#function calling
print("5+6=",add(5,6))
print("10+16=",add(10,16))
"""
***Output***
5+6= 11
10+16= 30
"""

Passing List as an Argument

We can also pass a list as an argument.


#Function definition
def fruits(fruitlist):
    for name in fruitlist:
     print("I like ",name)
mylist=["Mango","Orange","Apple"]
#function calling
fruits(mylist)
"""
***Output***
I like  Mango
I like  Orange
I like  Apple
"""

Arbitrary Arguments *args

If the number of arguments is unknown add asterisk(*) symbol before the parameter name.
We can access the arguments using index value.


#Function definition
def fruits(*fruitlist):
    print("I like ", fruitlist[0])
    print("I like ", fruitlist[1])
    print("I like ", fruitlist[2])
#function calling
fruits("Mango","Orange","Apple")
"""
***Output***
I like  Mango
I like  Orange
I like  Apple
"""

Function with pass statement

It is compulsory to define a function in python means we can not declare a function.
So to define a function with no content pass statement is used.


#function definition with no content
#using pass statement
def fruits(name):
    pass
#Function definition
def fruits(name):
    print("I like ", name)
#function calling
fruits("Mango")
"""
***Output***
I like  Mango
"""

Recursiont

The process of calling a function by itself is called recursion.
The benefit of recursion is that we can use it as a loop.


#Function definition
def myFunction():
    print("Hello")
    #function is calling by itself
    myFunction()
#function calling
myFunction()
"""
***Output***
Infinite time Hello
"""

Table of 5 using recursion


#Function definition
def table(no):
    if no<=50:
     print(no,end=" ")
     no=no+5
     #function is calling by itself
     table(no)
#function calling
table(5)
"""
***Output***
5 10 15 16 20 30 35 40 45 50 
"""

Factorial of any number using recursion


#Function definition
def factorial(no):
    if no>1:
     return  no*factorial(no-1)
    else:
     return 1
#taking user input
n=int(input("Enter any number:"))
#function calling
print("Factorial of ",n, " is ",factorial(n))
"""
***Output***
Enter any number:5
Factorial of  5  is  116
"""