Methods of set and frozenset that return new set or frozenset instances
return instances of subclasses, but these instances are not initialized
correctly.  In the attached code sample, z is an instance of MySet but
MySet.__new__ and MySet.__init__ are never called on it.  

It seems to me that such a method should return a fully-initialized
instance of the subclass.  Barring that, it should just return a set or
frozenset instance, not an instance of the subclass.

The bug is that the set operations return instances of the subclass,
rather than instances of set.

This is already fixed for 3.0: see issue 1721812.  It was deemed too risky 
to backport the change to 2.x.

In the sample code I attached, z is an instance of MySet under 3.0rc2.  Is 
that expected?

Thanks,
Alex

Mark Dickinson wrote:
> Mark Dickinson <dickinsm@gmail.com> added the comment:
> 
> The bug is that the set operations return instances of the subclass,
> rather than instances of set.
> 
> This is already fixed for 3.0: see issue 1721812.  It was deemed too risky 
> to backport the change to 2.x.
> 
> ----------
> assignee: theller -> 
> components: +Interpreter Core -ctypes
> nosy: +marketdickinson
> resolution:  -> duplicate
> status: open -> closed
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue4357>
> _______________________________________

Well, this was changed only three days ago.
Please wait for the next 3.0rc3...