MRO Error on Multiple Inheritance?

[Michele Simionato]

On Jan 4, 9:03 pm, Ming <min... at gmail.com> wrote:
> I'm working through Wesley Chun's CPP2e and got this error on 13.11.1,
> pp 548 where his interpreter snippet shows no problems:
>
> ActivePython 2.5.1.1 (ActiveState Software Inc.) b
> Python 2.5.1 (r251:54863, May  1 2007, 17:47:05) [
> win32
> Type "help", "copyright", "credits" or "license" f>>> class A(object): pass
> ...
> >>> class B(A): pass
> ...
> >>> class C(B): pass
> ...
> >>> class D(A, B): pass
>
> ...
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: Error when calling the metaclass bases
>     Cannot create a consistent method resolution
> order (MRO) for bases A, B
>
> (I submitted the problem to the author but I'm not sure I'll ever hear
> back.)  I'm guessing that this kind of diamond inheritance is
> prohibited by the interpreter, and that his lack of error messages
> from the interpretation is due to actually leaving out the "class
> B(A): pass"  Can someone shed light?  Thanks.

Yes, the MRO for new-style classes changed in Python 2.3, see
http://www.python.org/download/releases/2.3/mro/