Python decorators supports aspect-oriented programming. It is used to add or modify code in functions or classes. Using decorators will provide security, tracing, looking etc Let see an example:

@fundecorator
def myfunc():
print "This is my function"

The above example has a function myfunc() with a decorator @fundecorator . The symbol @ tell that the type of the name is a decorator. Some points regarding decorators: -- Decorators can be function or class -- The class that is used as a decorator must implement __call__ -- In a class decorator  arguments are optional whereas a function decorator must have arguments. Decorators are of two types: 1. Class decorators:- In this we use class as decorator to decorate functions/classes. For example:

>>> class mydecorator(object):
...   def __init__(self, f):
...     self.f = f
...   def __call__(self):
...     print "Start of", self.f.__name__
...     self.f()
...     print "End of", self.f.__name__
...
>>> @mydecorator
... def func1():

...   print "This is function 1"
...
>>> @mydecorator
... def func2():
...   print "This is function 2"
...

The output is:

>>> func1()
Start of func1
This is function 1
End of func1
>>> func2()
Start of func2
This is function 2
End of func2

Class decorators without arguments: The above example is considered under this category. There are no decorator arguments in __init__. So the control is passed to the constructor f() which will take the function to be decorated as input. __call__ will be invoked only after the decorated function is called. Class decorators with arguments: These are the class decorators which take input arguments. For example:

#decorators.py
class mydecorator(object):
def __init__(self, arg1, arg2, arg3):
self.arg1 = arg1
self.arg2 = arg2
self.arg3 = arg3
def __call__(self, f):
def sum_of_args(*args):
print("Decorator arguments:", self.arg1, self.arg2, self.arg3)
f(*args)
print("Sum of decorator arguments: ", (self.arg1+self.arg2+self.arg3))
return sum_of_args

@mydecorator(5, 10, 15)
def sayHello(a1, a2, a3, a4):
print('sayhello() arguments:', a1, a2, a3, a4)

print("Calling sayHello()")
sayHello("say", "hi", "hello", "world")

The output for the above program will be:

~$ python decorators.py
Calling sayHello()
('Decorator arguments:', 5, 10, 15)
('sayhello() arguments:', 'say', 'hi', 'hello', 'world')
('Sum of decorator arguments: ', 30)

2. Function decorators:- In this we use function as decorator to decorate functions/classes. For example:

>>> def mydecorator(f):
...   def myfun():
...     print "Start of", f.__name__
...     f()
...     print "End of", f.__name__
...   myfun.__name__ = f.__name__
...   return myfun
...
>>> @mydecorator
... def func1():
...   print "This is function 1"
...
>>> @mydecorator
... def func2():
...   print "This is function 2"
...

The output will be same as the output for Type 1.

Subscribe To our news letter

Subscribe to our news letter to receive latest blog posts into your inbox. Please fill your email address in the below form.
*We don't provide your email contact details to any third parties
Latest Comments
Related Articles
Understanding Python Properties Ramya Ambati

Python Properties is a class for managing class attributes in Python. Property( ) is a built-in function that creates and returns a property object

Syntax:
Continue Reading...

Python using yield and generators. Dinesh Deshmukh

Generators are memory efficient. They allow us to code with minimum intermediate arguments, less data structures.
Generators are of two types, generator expressions and generator ...

Continue Reading...
How to create pdf files in Python using Pdfkit Divya Sri

There are many approches for generating PDF in python. pdfkit is one of the better approache as, it renders HTML into PDF with various image ...

Continue Reading...