python - what is decorators

Python decorators 

USING FUNCTION AS DECORATOR

In simple words, it decorates (beautify)  a callable objects (function, methods or class)! In a technical word, it takes a callable object (say function ) and extends (decorate) behavior of called object.


Let us create a decorator function - new_decorator

decorator function
1- take another function as arguments - func_argument
2- have a wrapper function - wrap_func

2- return wrapper function - wrap_func


Decorator function is preceded with @ sign when called ( i is called pie syntax). It follow with the function need to be called - my_function


1 def new_decorator(func_argument):
2    
3    def wrap_func():
4        print 'Code here before executing function'
5        
6        # then execute function that has been passed
7        func_argument()
8        
9        print 'Code here will execute after function'
10        
11    return wrap_func()
12    
13 @new_decorator
14 def my_function():
15    print 'Hello, Ansari'

A decorator is equivalent to

my_function = new_decorator(my_function)

Output

Code here before executing function
Hello, Ansari

Code here will execute after function


Reference
- code url
- https://realpython.com/blog/python/primer-on-python-decorators/




Another Decorator  Example


def change_uppercase(f):
    """take a function f as argument and return function upper_case"""
    def upper_case(*args, **kwargs):
        x = f(*args, **kwargs)
        return x.upper()
    return upper_case



@change_uppercase
def print_string(s):
    return s



print_string("CaMelCaSe - this is Camel Case")
Out[49]: 'CAMELCASE - THIS IS CAMEL CASE'




code_url


 

USING CLASS AS DECORATOR

Code

class CallCount:
    def __init__(self, f):
        self.f = f
        self.count = 0

    def __call__(self, *args, **kwargs):
        self.count += 1
        return self.f(*args, *kwargs)

    def get_count(self):
        return self.count


@CallCount
def hello(name):

    print('Hello, {}'.format(name))

Output

hello.get_count()

Out[10]: 0

hello('d')

Hello, d

hello('a')

Hello, a

hello('b')

Hello, b

hello.get_count()

Out[14]: 3

Reference
- code url