instantiate all subclasses of a class

[Daniel Nogradi]

> > More precisely I have a module m with some content:
> >
> > # m.py
> > class A:
> >     pass
> > class x( A ):
> >     pass
> > class y( A ):
> >     pass
> > # all kinds of other objects follow
> > # end of m.py
> >
> > and then in another module I have currently:
> >
> > # n.py
> > import m
> > x = m.x( )
> > y = m.y( )
> > # end of n.py
> >
> > and would like to automate this in a way that results in having
> > instances of classes from m in n whose names are the same as the
> > classes themselves. But I only would like to do this with classes that
> > are subclasses of A.
> >
> > Any ideas?
>
> Just go through the objects in the module, test if they are classes,
> subclasses of `A` and not `A` itself:
>
> from inspect import isclass
> import test
>
> instances = dict()
> for name in dir(test):
>     obj = getattr(test, name)
>     if isclass(obj) and issubclass(obj, test.A) and obj is not test.A:
>         instances[name] = obj()


Thanks, this looks pretty good. However there is some wierdness with
isclass: whenever a class has a __getattr__ method an instance of it
will be detected by isclass as a class (although it is not).

>>> from inspect import isclass
>>>
>>> class x:
...     def __getattr__( self, attr ):
...         pass
...
>>> y = x( )
>>> isclass( y )
True
>>>

If there is no __getattr__ method isclass works as expected. Am I
misunderstanding something here or isclass should return False for any
instance of any class including those with a __getattr__ method?