[issue34282] Enum._convert shadows members named _convert

[Ethan Furman]

Ethan Furman <ethan at stoneleaf.us> added the comment:

For versions 3.6 and 3.7 the solution is to modify the shadow check at line 236 so only DynamicClassAttributes are /not/ shadowed (meaning the _convert method would be shadowed by an _convert member).

For 3.8 we can move _convert to the metaclass: I wasn't originally supportive of this idea, but I can see it being useful for other Enum mix-ins such as str.  However, I will want to include a check that such a mix-in is there -- probably by checking that the Enum type is a subclass of the first member's type... something like:

    if not issubclass(cls, members[0]):
       raise TypeError(...)
While we're making that change we can also check that members is not empty and issue a friendlier error message.

We can also rename _convert to _convert_ in 3.8, but we'll need to have _convert also on the metaclass and have it trigger a warning that _convert_ is now the right way, and _convert will go away in 3.9.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34282>
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