On Feb 9, 1:14 pm, Rouslan Korneychuk <rousl...@msn.com> wrote: > On 02/09/2011 02:42 PM, Carl Banks wrote: > > This is the only case I can think of where the > > layout conflict would be caused by a type setting tp_dictoffset. > > No, actually I have code that is roughly equivalent to the following > pseudocode: > > class _internal_class(object): > __slots__ = () > > class BaseA(_internal_class): > __slots__ = (some_data,...,__weaklist__,__dict__) > > class BaseB(BaseA): > __slots__ = (some_data,...,__weaklist__,__dict__) > > class BaseC(_internal_class): > __slots__ = (some_other_data,...,__weaklist__,__dict__) > > class Derived(BaseB,BaseC): > __slots__ = (combined_data,...,__weaklist__,__dict__)
Ah, ok. So BaseA sticks weaklist and dict into a certain layout location. BaseB gets the same location because it has the same layout. BaseC sticks weaklist and dict into a different location. Derived then can't reconcile it because dict and weakref are in different locations. Again, for the reasons I mentioned the layouts conflict even if you set tp_weakreflist and tp_dictoffset. > Before adding the weaklist and instance dicts, this all worked fine. > _internal_class was necessary to prevent the "lay-out conflict" error. That actually seems like an error to me. It should signal a conflict if bases have different layout sizes from their own base, and one isn't a base of the other, which wouldn't be the case here. "some_data" a proper subset of "some_other_data", right? (If it isn't you have worse problems than dict and weakreflist.) A more natural way to handle this situation would be to place common slots in the internal_class. But we'll just accept it for now. > But when I added them to every class except _internal_class, I got the > error. I tried adding the dicts to _internal_class and it worked again. > (The classes are set up like this because the code is from my unit-test > code.) Don't set tp_dictoffset and tp_weakrefoffset in any of the bases. Set them only in Derived. If you need to instantiate a Base, make a trivial dervied class for it. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
