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 13:21:02 CET 2012


On Saturday, March 17, 2012 6:04:58 PM UTC+8, Cosmia Luna wrote:
> 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

Oh I'm wrong.
If I use a decorator, the decorator will NEVER get the owner class even in Python 2.X. The function is just plain function instead of unbound method before the code of a class is fully evaluated. So the decorator ALWAYS receives a plain function.

I'll look into the module inspect and try to get the frame of calling...

Cosmia



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