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typing_extensions.NewType annotations are not recognized on < 3.10 (regression in 1.4.0) #16297

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gschaffner opened this issue Oct 20, 2023 · 0 comments · Fixed by #16298
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typing_extensions.NewType annotations are not recognized on < 3.10 (regression in 1.4.0) #16297

gschaffner opened this issue Oct 20, 2023 · 0 comments · Fixed by #16298
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bug mypy got something wrong topic-newtype NewType

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@gschaffner
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Bug Report

Mypy 1.4.0 introduced a regression where typing_extensions.NewType annotations are not correctly recognized when --python-version < 3.10.

this bisects to python/typeshed@a6d0aaf via python/typeshed#10205 via #15334. however this does not appear to be a typeshed issue; it's just that the typeshed change exposed a previously-hidden Mypy issue.

To Reproduce

# run with --python-version=3.9 or below, using mypy d11db28 or 1.4 or later

from typing_extensions import NewType

N = NewType("N", int)

x: N  # error: Variable "eg_newtype.N" is not valid as a type  [valid-type]

Expected Behavior

Mypy passes this example.

Actual Behavior

Mypy fails this example; see above.

Your Environment

  • Mypy version used: 1.6.1 (compiled) and current master (uncompiled)
  • Mypy command-line flags: --python-version=3.9
  • Mypy configuration options from mypy.ini (and other config files): none (i.e. using vendored typeshed)
  • Python version used: 3.12
@gschaffner gschaffner added the bug mypy got something wrong label Oct 20, 2023
@gschaffner gschaffner mentioned this issue Oct 20, 2023
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@AlexWaygood AlexWaygood added the topic-newtype NewType label Oct 20, 2023
@hauntsaninja hauntsaninja mentioned this issue Oct 20, 2023
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ilevkivskyi pushed a commit that referenced this issue Oct 20, 2023
@gschaffner
Correctly recognize typing_extensions.NewType (#16298)
eecbcb9 
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fixes #16297.

since the `.+_NAMES` constants in `types.py` are each referenced
multiple times while other examples like this (i.e. a `.+_NAMES`
tuple/set used only once) are inlined, I've inlined this one.
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Correctly recognize typing_extensions.NewType
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@gschaffner @AlexWaygood