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:
>
> * Define a new type flag Py_TPFLAGS_INSTANCE.
> * Create a new predicate Py_IsInstance which checks for this
> flag.
> * Set this flag on PyInstance_Type.
> * Replace most occurances of PyInstance_Check with
> Py_IsInstance.
>
> Extension types (like ExtensionClass) can then define the type
> flag Py_TPLAGS_INSTANCE and be treated as an instance type by the
> Python interpreter. This should make it quite a bit easier to make
> extension types behave like "real" classes.
>
> Comments?
Sounds fine, except that the "isinstance()" behaviour would
have to be defined somewhere / somehow... a mapping of slots
to __special_methods__ would be a good start.
BTW, mxProxy does some of this mapping already... you may want to
have a look.
--
Marc-Andre Lemburg
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Business: http://www.lemburg.com/
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