[issue44919] TypedDict subtypes ignore any other metaclasses in 3.9+

[Łukasz Langa]

Łukasz Langa <lukasz at langa.pl> added the comment:

The change to disallow this in Python 3.9 was deliberate, see BPO-40187 and its description.

Your attempt to make `isinstance()` work with TypedDict subclasses goes directly against this design. In fact, PEP 589 explicitly says that:

- Methods are not allowed, since the runtime type of a TypedDict object will always be just dict (it is never a subclass of dict).
- Specifying a metaclass is not allowed.

I'm -1 to allow this but I'll also wait for Serhiy to voice his opinion.

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nosy: +lukasz.langa, serhiy.storchaka

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