confusion with decorators

88888 Dihedral dihedral88888 at googlemail.com
Fri Feb 1 12:26:27 CET 2013


Jason Swails於 2013年1月31日星期四UTC+8上午8時34分03秒寫道:
> Hello,
> 
> 
> I was having some trouble understanding decorators and inheritance and all that.  This is what I was trying to do:
> 
> 
> 
> # untested
> class A(object):
>    def _protector_decorator(fcn):
> 
>       def newfcn(self, *args, **kwargs):
>          return fcn(self, *args, **kwargs)
>       return newfcn
> 
> 
> 
>    @_protector_decorator
>    def my_method(self, *args, **kwargs):
>       """ do something here """
> 
> 
> 
> class B(A):
>    def _protector_decorator(fcn):
>       def newfcn(self, *args, **kwargs):
> 
>          raise MyException('I do not want B to be able to access the protected functions')
>       return newfcn
> 
> 
> 
> The goal of all that was to be able to change the behavior of my_method inside class B simply by redefining the decorator. Basically, what I want is B.my_method() to be decorated by B._protector_decorator, but in the code I'm running it's decorated by A._protector_decorator.
> 
> 
> 
> I presume this is because once the decorator is applied to my_method in class A, A.my_method is immediately bound to the new, 'decorated' function, which is subsequently inherited (and not decorated, obviously), by B.
> 
> 
> 
> Am I correct here?  My workaround was to simply copy the method from class A to class B, after which B._protector_decorator decorated the methods in B.  While this doesn't make the use of decorators completely pointless (the decorators actually do something in each class, it's just different), it does add a bunch of code duplication which I was at one point hopeful to avoid.
> 
> 
> 
> I'm still stumbling around with decorators a little, but this exercise has made them a lot clearer to me.
> 
> 
> Thanks!
> Jason

It sounds that you need a decorator mapper to 
perform the functionality of your designs.




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