# 你的第一個裝飾器 # 你的第一個裝飾器 在上一個例子里，其實我們已經創建了一個裝飾器！現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？我們剛剛應用了之前學習到的原理。這正是python中裝飾器做的事情！它們封裝一個函數，并且用這樣或者那樣的方式來修改它的行為。現在你也許疑惑，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。這里是我們如何使用@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輸出應該是“a_function_requiring_decoration”。這里的函數被warpTheFunction替代了。它重寫了我們函數的名字和注釋文檔(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 ~~~ 現在好多了。我們接下來學習裝飾器的一些常用場景。 藍本規范: ~~~ 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接受一個函數來進行裝飾，并加入了復制函數名稱、注釋文檔、參數列表等等的功能。這可以讓我們在裝飾器里面訪問在裝飾之前的函數的屬性。