Python's method-resolution algorithm: An implementation question

[Evan Aad]

Thanks!

On Tue, Aug 15, 2017 at 10:41 PM, Ian Kelly <ian.g.kelly at gmail.com> wrote:
>
> On Tue, Aug 15, 2017 at 12:57 PM, Evan Aad <oddeveneven at gmail.com> wrote:
> > I don't see how, since the L(B*)'s are listed in order in the argument
> > list: L(B1), L(B2), ..., and each L(B*) starts with B*: L(B1) = <B1,
> > ...>, L(B2) = <B2, ...>, ...
> >
> > Could you please give a counter-example?
>
> Sure.
>
> merge(<B1, A1>, <B2, A2, B1>)  ->  <B2, B1, A1, A2>
>
> vs:
>
> merge(<B1, A1>, <B2, A2, B1>, <B1, B2>)  ->  TypeError
>
> Or in Python:
>
> >>> class A1: pass
> >>> class A2: pass
> >>> class B1(A1): pass
> >>> class B2(A2, B1): pass
> >>> class C(B1, B2): pass
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: Cannot create a consistent method resolution order (MRO)
> for bases B1, B2
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