[Python-Dev] Odd new-style class __new__ behavior

[Kevin Jacobs]

On 30 Mar 2002, Michael Hudson wrote:
> Kevin Jacobs <jacobs@penguin.theopalgroup.com> writes:
> > Suppose I define:
> > 
> > class Foo(object):
> >   def __new__(cls):
> >     return 1
> > 
> > class Bar(object):
> >   def __new__(cls):
> >     return [1,2,3]
> > 
> > Python 2.2 returns:
> >   print Foo()
> >   > 1
> >   print Bar()
> >   > []
> > 
> > I would expect that Bar() should return [1,2,3].  Am I running into some
> > clever undocumented feature or a bug?  
> 
> Is tp_init being called on the returned list?

I suspect that the object construction code would check the result of tp_new
to see if the expected type.  If not, tp_init should not be called on the
instance.  I suspect that this check must already be there, or else none of
these cases would work at all.

Anyhow, I won't know what is really happening for sure until Monday, when I
can run this through gdb.  However, some more data points: returning
dictionaries, tuples, strings, classic object instances, and user-defined
new-style classes all seem to work.  Only lists seem to behave this way.

Guido, can you clarify what the "correct behavior" should be for the above
cases?  Once I know that, I will happily supply a corrective patch if one is
necessary.

Regards,
-Kevin

--
Kevin Jacobs
The OPAL Group - Enterprise Systems Architect
Voice: (216) 986-0710 x 19         E-mail: jacobs@theopalgroup.com
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