python decorator syntax sugar

Summary:

Decorator (Decorators) is an important part of Python. Simply put: they are modified functional capabilities of other functions.

For example, we write flask, the route is to use a decorator defined. If write access control, the access control is generally realized by a decorator. Logging, generally may be implemented by decorators.

Simply put, it is to increase the practice of certain functions to one or several functions.

The following example implementation.

A: basic functions

1. Source

from time import sleep


def watch_movie():
    print('看电影')
    sleep(3)
    print('The End')


if __name__ == '__main__':
    watch_movie()

View Code

2. Perform results

The code is simple, first print cinema, an interval of 3 seconds to print The End.

Two: decorator principle

1. Goal: compute a function of time

2. Source

from time import sleep, time


def ceal_time():
    before = time()
    watch_movie()
    after = time()
    print('函数运行%s秒' % (after - before))


def watch_movie():
    print('看电影')
    sleep(3)
    print('The End')


if __name__ == '__main__':
    ceal_time()

View Code

3. Perform results

The code is simple, first print cinema, an interval of 3 seconds to print The End, then print run timing function.

4. Analysis

We put a function into another function to run, which is the basic principle of the decorator.

Three: the transformation of timing functions as a generic function

1. Objective: to calculate a function of time this function, adapted to different functions.

2. Source

from Time Import SLEEP, Time 


DEF ceal_time (Fun): 
    before = Time () 
    Fun () 
    After = Time ()
     Print ( ' function running% s s ' % (After - before)) 


DEF watch_movie ():
     Print ( ' see film ' ) 
    SLEEP ( 3 )
     Print ( ' at The End ' ) 


DEF play_game ():
     Print ( ' playing games ' ) 
    SLEEP (3)
    print('Game Over')


if __name__ == '__main__':
    ceal_time(watch_movie)
    ceal_time(play_game)

View Code

3. Perform results

Watching movies and playing games two functions are carried out.

4. Analysis

We can function as an object, which passed in another function.

Four: become a decorator

1. Objectives:

We changed the function is called, can not fail to change the function code in the position to call it?

2. Source:

from time import sleep, time


def ceal_time(fun):
    def wrapper():
        before = time()
        fun()
        after = time()
        print('函数运行%s秒' % (after - before))

    return wrapper


@ceal_time
def watch_movie():
    print('看电影')
    sleep(3)
    print('The End')


# @ceal_time
def play_game():
    print('玩游戏')
    sleep(3)
    print('Game Over')


if __name__ == '__main__':
    watch_movie()
    play_game()

View Code

3. Perform results

Look in front of the movie plus a decorator to achieve the function run time, play games without adding decorator, so there is no timing function runs.

And in the main function is called and did not increase in the same decorators.

Five: Functions have arguments

1. Objectives: function to be decorated, with a processing parameter

2. Source:

from Time Import SLEEP, Time 


DEF ceal_time (Fun):
     DEF warpper (* args, ** kwargs):   # modified 
        before = Time () 
        Fun ( * args, ** kwargs)   # modifications 
        After = Time ()
         Print ( ' function second running% s ' % (After - before)) 

    return warpper 


@ceal_time 
DEF watch_movie (name, movie):
     Print ( ' % s% s watching movies ' % (name, movie)) 
    SLEEP ( . 3 )
    Print ( ' of The End ' ) 


# @ceal_time 
DEF play_game (name, Game):
     Print ( ' % s% s game play ' % (name, Game)) 
    SLEEP ( . 3 )
     Print ( ' Game Over ' ) 


IF  the __name__ = = ' __main__ ' : 
    watch_movie (name = " John Doe " , Movie = " cat and mouse " ) 
    play_game (name = ' John Doe ', Game = ' Warcraft ' )