Python Advanced - Decorator

Python Advanced - Decorator Introduction:

Python Advanced - Decorator.It is a function that adds extra functionality to an existing function, which is essentially a closure function.

1. Python Advanced - Decorator.Definition of decorator
It is a function that adds extra functionality to an existing function, which is essentially a closure function .
Decorator features:
1.Do not modify the source code of existing functions
2.Do not modify the calling method of existing functions
3.Add extra functionality to an existing function

2. Python Advanced - Decorator.Sample code for the decorator

# Add a login verification function
def check( fn ):
def inner( ):
print("Please login first...")
fn ( )
return inner
def comment( ):
print("Post a comment")
# Use decorators to decorate functions
comment = check(comment)
comment( )
#Basic prototype of the decorator
# def decorator( fn ): # fn : target function.
# def inner( ):
# '''Before executing the function'''
# fn () # Execute the decorated function
# '''After executing the function'''
# return inner
Code Description:
•The closure function has one and only one parameter, which must be a function type, so that the function defined in this way is a decorator.
•Writing code should follow the open and closed principle, which stipulates that the functional code that has been implemented is not allowed to be modified, but can be extended.
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3. Python Advanced - Decorator.Syntax sugar for decorators

If there are multiple functions that need to add the function of login verification, each time you need to write code like func = check( func ) to decorate the existing functions, which is still rather troublesome.
Python provides a simpler way to write decorative functions, which is syntactic sugar. The writing format of syntactic sugar is: @decorator name , and the decoration of existing functions can also be completed by means of syntactic sugar.
# Add a login verification function
def check( fn ):
print("The decorator function is executed")
def inner( ):
print("Please login first...")
fn ( )
return inner
# Use syntactic sugar to decorate functions
@check
def comment( ):
print("Post a comment")
comment( )
illustrate:
•@check is equivalent to comment = check(comment)
•The execution time of the decorator is as soon as the module is loaded.
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4.Python Advanced - Decorator.Summary
•decorator is essentially a closure function that extends an existing function with additional functionality.
•The syntax of the decorator is :
# decorator
# def decorator( fn ): # fn : The decorated target function.
# def inner( ):
# '''Before executing the function'''
# fn () # Execute the decorated target function
# '''After executing the function'''
# return inner
The syntax sugar usage of decorators: @ decorator name , which can also complete the decoration operation on existing functions.