Python Decorators

Decorators are used to modify the existing functionality without changing the existing code of that function. A function is modify with another function at compile time is also called as meta programming

Simple Decorators

Like the below example, we can implement the decorators for the normal function to implement more functionality

#Normal Function without decorators
def school_name(name):
    print("The school name is {}".format(name))

school_name("Rathna Schools")

Output

The school name is Rathna Schools

Incase, business request to implement pretty text for the existing function means, we can develop decorator like below to extend its functionality without modification in it

#Decorator Implementation
def simple_decorator(func):
    def make_pretty(input_data):
        print("Make Pretty - Implementation")
        func(input_data)
    return make_pretty

@simple_decorator
def school_name(name):
    print("The school name is {}".format(name))

school_name("Rathna Schools")

Output

Make Pretty - Implementation
The school name is Rathna Schools

Realtime Example 1

Implementation of exception handling decorators like the below example to handle exception

#Normal function without any exception
def divide(dividend, divisor):
    print("The quotient is {}".format(str(dividend//divisor)))
    print("The remainder is {}".format(str(dividend%divisor)))

#This work without any exception
divide(100,3)

#This raise zero division exception
divide(75, 0)

Output

The quotient is 33
The remainder is 1
Traceback (most recent call last):
File "<string>", line 7, in <module>
File "<string>", line 3, in divide
ZeroDivisionError: integer division or modulo by zero

Handle above exception with decorators without any modification in existing function

#Exception handling decorators
def exception_handler(func):
    def inner_func(num1, num2):
        try:
            func(num1, num2)
        except ZeroDivisionError:
            print("Divisor should not be Zero")
    return inner_func

@exception_handler
def divide(dividend, divisor):
    print("The quotient is {}".format(str(dividend//divisor)))
    print("The remainder is {}".format(str(dividend%divisor)))

#This work without any exception
divide(100,3)

#Now this handles by exception handler decorator
divide(75, 0)

Output

The quotient is 33
The remainder is 1
Divisor should not be Zero

Realtime Example 2

Database connection decorator implementation for the required function to perform the database operation like the below example

#DB connector decorator
def make_connection(func):
    def inner_func(*args, **kwargs):
        print("DB connection - Successful")
        func(*args, **kwargs)
    return inner_func

@make_connection
def read_user(*args, **kwargs):
    query = "select * from {} where id={}".format(args[0], kwargs['user_id'])
    print(query)

read_user("users", user_id="1234")

Output

DB connection - Successful
select * from users where id=1234