Decorator question

Peter Otten __peter__ at web.de
Sat Oct 16 16:49:50 CEST 2010


Lucasm wrote:

> I have a decorator problem and hope someone is able to help me out/
> assist me. Thanks in advance.
> 
> Suppose:
> ### Begin some_library_module ###
> 
> def some_decorator(some_method):
>     def inner(an_arg, *args, **kwargs):
>         return some_method(an_arg, *args, **kwargs)
>     return inner
> 
> ### End some_library_module ###
> 
> ### Begin my_module ###
> 
> def my_decorator(some_method):
>     def inner(self, an_arg, *args, **kwargs):
>         self.do_something()

At this point some_method() is just a Python function. You have to build a 
bound method or at least something that "knows" about self before you pass 
it on:

          bound_method = some_method.__get__(self)
          # bound_method = new.instancemethod(some_method, self)
          # bound_method = functools.partial(some_method, self)
          return some_decorator(bound_method)(an_arg, *args, **kwargs)

>     return inner
> 
> 
> class My_Class(object):
>     @my_decorator
>     def my_method(self, an_arg, *args, **kwargs):
>         print self, an_arg
> 
>     def do_something(self):
>         pass
> 
> ### End My_module ###
> 
>>>> My_Class().my_method('bla')
> TypeError: my_method() takes at least 2 arguments (1 given)
> 
> `self` is lost in the process, because my decorator does use it and
> the library's doesn't. I fail to  find a way to keep self in the args
> without modifying the library.




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