How to get a reference of the 'owner' class to which a method belongs in Python 3.X?

Cosmia Luna cosmius at gmail.com
Sat Mar 17 11:04:58 CET 2012


On Saturday, March 17, 2012 5:25:06 PM UTC+8, Peter Otten wrote:
> Cosmia Luna wrote:
> 
> > I'm porting my existing work to Python 3.X, but...
> > 
> > class Foo:
> >     def bar(self):
> >         pass
> > 
> > mthd = Foo.bar
> > 
> > assert mthd.im_class is Foo # this does not work in py3k
> > 
> > So, how can I get a reference to Foo? This is important when writing
> > decorators, the only way I can think out is:
> > 
> > class Foo:
> >     def bar(self):
> >         'Foo' # manually declare the owner class
> >         pass
> > 
> > mthd = Foo.bar
> > 
> > assert mthd.__globals__[mthd.__doc__] is Foo # this works
> > 
> > class Child(Foo):
> >     def bar(self):
> >         'Child' # I have to override all method defined by bar but do
> >         nothing pass
> > 
> > child_mthd = Child.bar
> > 
> > assert child_mthd.__globals__[child_mthd.__doc__] is Child # this works
> > 
> > But the code above is quite ugly and abuses the __doc__. Is there any
> > equivalent in py3k of im_class?
> 
> class set_class:
>     def __init__(self, method):
>         self.method = method
>     def __get__(self, instance, class_):
>         if instance is None:
>             method = self.method
>             def f(*args, **kw):
>                 return method(*args, **kw)
>             f.im_class = class_
>             f.__name__ = method.__name__
>             return f
>         return self.method.__get__(instance, class_)
>     
> class Foo:
>     def __init__(self, name):
>         self.name = name
>     @set_class
>     def bar(self):
>         print("%s says hello from bar()" % self)
>     def __str__(self):
>         return self.name
> 
> class Bar(Foo):
>     pass
> 
> assert Foo.bar.im_class is Foo
> assert Bar.bar.im_class is Bar
> 
> Foo("Fred").bar()
> Foo.bar(Foo("Fred"))
> 
> Bar("Fred").bar()
> Bar.bar(Bar("Fred"))
> 
> The cleaner approach is probably:
> 
> Rule('/<action>/', endpoint=(RootController, RootController.otheraction))
> ...
> Controller, method = endpoint
> controller = Controller(Request(environ))
> ...
> method(controller)


That's exactly what I want, and I think you're right, the approach below is cleaner.
Rule('/<action>/', endpoint=(RootController, RootController.otheraction)).

Thanks a lot.
Cosmia



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