Ed Leafe wrote: > In Dabo, we create cursor classes that combine the backend-specific > dbapi cursor class with our own mixin class that adds framework- > specific behaviors. This has been working well for a couple of years > now with many different backends, but today I'm getting errors with our > Firebird class. I've checked the kinterbasdb site, and found nothing > there that was helpful. The error reads: > > TypeError: Error when calling the metaclass bases > type 'kinterbasdb.Cursor' is not an acceptable base type > > Here's some simple code that will generate the error: > > import kinterbasdb > KCursor = kinterbasdb.Cursor > > class TestMixin(object): pass > # This next line will raise the error. > class CombinedCursor(TestMixin, KCursor): pass > myCursor = CombinedCursor() > > I'm not sure exactly what this error message means, so I don't know > how to go about fixing it.
I have no clue but googling 'type is not an acceptable base type' finds this thread http://groups.google.com/group/comp.lang.python/browse_thread/thread/628b8ad34a36db17/579f716b143f4967%23579f716b143f4967?sa=X&oi=groupsr&start=0&num=3 which points to the Py_TPFLAGS_BASETYPE. This example http://www.python.org/doc/2.3.5/ext/node22.html shows that flag being set to indicate that an extension class may be subclassed; the API docs confirm this: http://docs.python.org/api/type-structs.html#l2h-968 So it looks like kinterbasdb.Cursor is a C extension class that may not be subclassed because Py_TPFLAGS_BASETYPE is not set. Whether this is by design or accident would be a question for the kinterbasdb developers. One workaround might be to use delegation instead of subclassing... Kent -- http://mail.python.org/mailman/listinfo/python-list
