Context manager with class methods

[Gregory Ewing]

Terry Reedy wrote:

> it is normal to look for special methods on the class (and superclasses)
 > of an object rather than starting with the object itself.

> I suspect there was a deliberate change to correct an anomaly, though 
> this might have been done as part of some other change.

It's a necessary consequence of the fact that new-style classes
are also instances. Without it, there would be an ambiguity as
to whether a special method defined the behaviour of instances
of a class or of the class object itself.

It also increases efficiency, because for those special methods
that correspond to C-level type slots, you only have to look
in the type slot to find an implementation of the method,
rather than having to look in the instance dict first.

-- 
Greg