On 21 November 2017 at 11:09, Neil Girdhar <[email protected]> wrote:
>
> On Sat, Nov 18, 2017 at 9:29 PM Nick Coghlan <[email protected]> wrote:
>>
>> >>> class C: pass
>> ...
>> >>> class S(C): pass
>> ...
>> >>> class E: pass
>> ...
>> >>> class B(S, E): pass
>> ...
>> >>> class R(E, C): pass
>> ...
>> >>> class Z(B, S, R, E, C): pass
>> ...
>> Traceback (most recent call last):
>> File "<stdin>", line 1, in <module>
>> TypeError: Cannot create a consistent method resolution order
>> (MRO) for bases C, E
> Sorry, I wrote back too quickly. I meant also to change B's requested MRO
> to be:
>
> (B, S, E, C)
>
> It works with that change.
Right, but once you do that, then the existing resolver is already
able to handle things:
>>> class C: pass
...
>>> class S(C): pass
...
>>> class E: pass
...
>>> class B(S, E, C): pass
...
>>> class R(E, C): pass
...
>>> class Z(B, R): pass
...
>>>
If you wanted to pick up cases where two classes generate inconsistent
MROs that will prevent mutual subclasses (like "class B(S, E)" vs
"class R(E, C)"), that feels like a job for a type checker, since it
isn't obvious whether it's the definition of B or the definition of R
that should be changed to reorder their MRO.
Cheers,
Nick.
--
Nick Coghlan | [email protected] | Brisbane, Australia
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