te 4.7.0 breaks Mypy daemon on Python 3.7 (TypeError: metaclass conflict)

[NiklasRosenstein]

Using typing-extensions 4.7.0 on Python 3.7 breaks the Mypy daemon:

$ dmypy run src/
Traceback (most recent call last):
  File "mypy/dmypy/client.py", line 274, in main
  File "mypy/dmypy/client.py", line 394, in do_run
  File "mypy/dmypy/client.py", line 350, in start_server
  File "mypy/dmypy_server.py", line 35, in <module>
    from mypy.suggestions import SuggestionEngine, SuggestionFailure
  File "mypy/suggestions.py", line 86, in <module>
    class PyAnnotateSignature(TypedDict):
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

Pinning typing-extensions 4.6.3 fixes this error. It seems like a break in backwards compatibility in typing-extensions.

[JelleZijlstra]

This was fixed in mypy recently (python/mypy#15543) but not released. Given that 3.7 has reached its end of life, we're not planning to fix this in typing-extensions.

[NiklasRosenstein]

Thanks for the fast response.

Could you tell me why typing-extension 4.7.0 is stilled tagged with requires-python = ">=3.7" then? Would it make sense to yank 4.7.0 and 4.7.1 and update that to >=3.8?

[JelleZijlstra]

typing-extensions 4.7 generally works fine with Python 3.7. It's broken only when using dmypy (not mypy itself, which apparently doesn't use any TypedDict), or potentially with other mypyc-compiled applications that use TypedDict. A relatively obscure case in a single third-party tool on a version that has reached end of life isn't enough to justify yanking the release.