python中的装饰器

Question

我想了解装饰器的功能。我在下面的代码中做错了什么。请纠正它

正如我了解，当aFunction（）被调用时，它又调用myDecorator（），它也调用afunction（）。对？

另外如何传递参数代入机能缺失（）

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，则__call__方法需要调用它。事情是这样的：

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) 

与装饰会发生什么情况是，原来的功能是取代与任何装饰的回报。但是，您的原始代码并未保存对aFunction的任何引用，因此它已丢失。

Answer 2

您的__call__方法缺少您给aFunction的参数。这里

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()