在上一個例子里，其實我們已經(jīng)創(chuàng)建了一個裝飾器！現(xiàn)在我們修改下上一個裝飾器，并編寫一個稍微更有用點的程序：

def a_new_decorator(a_func):

    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()")

        a_func()

        print("I am doing some boring work after executing a_func()")

    return wrapTheFunction

def a_function_requiring_decoration():
    print("I am the function which needs some decoration to remove my foul smell")

a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"

a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()

a_function_requiring_decoration()
#outputs:I am doing some boring work before executing a_func()
#        I am the function which needs some decoration to remove my foul smell
#        I am doing some boring work after executing a_func()

你看明白了嗎？我們剛剛應(yīng)用了之前學(xué)習(xí)到的原理。這正是python中裝飾器做的事情！它們封裝一個函數(shù)，并且用這樣或者那樣的方式來修改它的行為?，F(xiàn)在你也許疑惑，我們在代碼里并沒有使用@符號？那只是一個簡短的方式來生成一個被裝飾的函數(shù)。這里是我們?nèi)绾问褂聾來運行之前的代碼：

@a_new_decorator
def a_function_requiring_decoration():
    """Hey you! Decorate me!"""
    print("I am the function which needs some decoration to "
          "remove my foul smell")

a_function_requiring_decoration()
#outputs: I am doing some boring work before executing a_func()
#         I am the function which needs some decoration to remove my foul smell
#         I am doing some boring work after executing a_func()

#the @a_new_decorator is just a short way of saying:
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)

希望你現(xiàn)在對Python裝飾器的工作原理有一個基本的理解。如果我們運行如下代碼會存在一個問題：

print(a_function_requiring_decoration.__name__)
# Output: wrapTheFunction

這并不是我們想要的！Ouput輸出應(yīng)該是“a_function_requiring_decoration”。這里的函數(shù)被warpTheFunction替代了。它重寫了我們函數(shù)的名字和注釋文檔(docstring)。幸運的是Python提供給我們一個簡單的函數(shù)來解決這個問題，那就是functools.wraps。我們修改上一個例子來使用functools.wraps：

from functools import wraps

def a_new_decorator(a_func):
    @wraps(a_func)
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()")
        a_func()
        print("I am doing some boring work after executing a_func()")
    return wrapTheFunction

@a_new_decorator
def a_function_requiring_decoration():
    """Hey yo! Decorate me!"""
    print("I am the function which needs some decoration to "
          "remove my foul smell")

print(a_function_requiring_decoration.__name__)
# Output: a_function_requiring_decoration

現(xiàn)在好多了。我們接下來學(xué)習(xí)裝飾器的一些常用場景。

藍本規(guī)范:

from functools import wraps
def decorator_name(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        if not can_run:
            return "Function will not run"
        return f(*args, **kwargs)
    return decorated

@decorator_name
def func():
    return("Function is running")

can_run = True
print(func())
# Output: Function is running

can_run = False
print(func())
# Output: Function will not run

注意：@wraps接受一個函數(shù)來進行裝飾，并加入了復(fù)制函數(shù)名稱、注釋文檔、參數(shù)列表等等的功能。這可以讓我們在裝飾器里面訪問在裝飾之前的函數(shù)的屬性。