[Python-Dev] A small step to removing the type/class split

Jim Fulton jim@digicool.com
Wed, 25 Oct 2000 08:25:53 -0400

Neil Schemenauer wrote:
> I've run into a problem with ExtensionClass which I believe can
> only be fixed by modifying Python.  I will try to explain.
> I have an ExtensionClass which defines __cmp__.  Depending on the
> objects being compared, the __cmp__ method may never be called.
> This is due to code in object.c that looks like this:
>     if (PyInstance_Check(v) || PyInstance_Check(w)) {
>         try to use use __cmp__ method
>     }
>     else {
>         try number coerce and fall back on type name comparison
>     }
> Extension classes can never pass the PyInstance_Check predicate.
> I've searched for all occurances of PyInstance_Check in the 2.0
> source.  In many places that PyInstance_Check occurs a more
> general "is this an instance-like type" check would seem to be
> more suitable.
> Here is my proposal:


I think you got some good answers later in the thread.

I'll point out that a work around is to make your ExtensionClass
a numeric type.  Numeric types have different comparison 
semantics that allow you to get around this limitation.
I did this a few months back for acquisition wrappers.


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