python中的裝飾器

Question

我想了解裝飾器的功能。我在下面的代碼中做錯了什麼。請糾正它

正如我瞭解，當aFunction（）被調用時，它又調用myDecorator（），它也調用afunction（）。對？

另外如何傳遞參數代入機能缺失（）

class myDecorator(object): 

    def __init__(self, f): 
     print "inside myDecorator.__init__()" 
     f(1) # Prove that function definition has completed 

    def __call__(self): 
     print "inside myDecorator.__call__()" 

@myDecorator 
def aFunction(*a): 
    print a 
    print "inside aFunction()" 

print "Finished decorating aFunction()" 

aFunction(2) 

Answer 1

f，在__init__，需要保存，則__call__方法需要調用它。事情是這樣的：

class myDecorator(object): 
    def __init__(self, f): 
     print "inside myDecorator.__init__()" 
     self.f = f 
     print "function has been saved" 
    def __call__(self, *args): 
     print "inside myDecorator.__call__()" 
     result = self.f(args) 
     print "done with f()" 
     return result 

@myDecorator 
def aFunction(*a): 
    print a 
    print "inside aFunction()" 

aFunction(1) 

與裝飾會發生什麼情況是，原來的功能是取代與任何裝飾的回報。但是，您的原始代碼並未保存對aFunction的任何引用，因此它已丟失。

Answer 2

您的__call__方法缺少您給aFunction的參數。這裏

class myDecorator(object): 

    def __init__(self, f): 
     print "inside myDecorator.__init__()" 
     f(1) # Prove that function definition has completed 
     self.__function = f 

    def __call__(self, *args): 
     # the *args magic is here to mirror the original parameter list of 
     # the decorated function. But it is better to place here parameter list 
     # of the function you want to decorate, in order to minimize error possibilities 
     print "inside myDecorator.__call__()" 
     return self.__function(*args) 

@myDecorator 
def aFunction(*a): 
    print a 
    print "inside aFunction()" 

print "Finished decorating aFunction()" 

aFunction(1) 
aFunction('a', 23, 42) 

Answer 3

class myDecorator(object): 

    def __init__(self, f): 
     print "inside myDecorator.__init__()" 
     # save a reference to the real function, so it can be called later 
     self.f = f 

    def __call__(self, *args, **kwargs): 
     print "inside myDecorator.__call__()" 
     # call the real function and return its result 
     # passing it any and all arguments 
     return self.f(*args, **kwargs) 

@myDecorator 
def aFunction(*a): 
    print a 
    print "inside aFunction()" 

print "Finished decorating aFunction()" 

aFunction(1) 

print "Finished calling aFunction()