8000 Incorrect types for `keyword.kwlist` and `keyword.softkwlist` · Issue #9679 · python/typeshed · GitHub
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Eclips4 opened this issue Feb 4, 2023 · 5 comments · Fixed by #9680
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Incorrect types for keyword.kwlist and keyword.softkwlist #9679

Eclips4 opened this issue Feb 4, 2023 · 5 comments · Fixed by #9680

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@Eclips4
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Eclips4 commented Feb 4, 2023

For some reason, kwlist and softkwlist typed as Sequence[str] instead of list[str]
Corresponding to Lib/keyword.py, it's pure lists.
@Eclips4 Eclips4 changed the title Incorrect types for keywords.kwlist and keywords.softkwlist Incorrect types for keyword.kwlist and keyword.softkwlist Feb 4, 2023
@Eclips4 Eclips4 mentioned this issue Feb 4, 2023
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@TeamSpen210
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This is probably intentional - these attributes are supposed to be constants, and really shouldn't be modified. Annotating them as Sequence will make the type checker flag any modification attempts. Could do with having a comment to mention that, and also making them Final[Sequence[str]].

@Eclips4
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Eclips4 commented Feb 5, 2023 •
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Thank you!
I think, it's good idea to making them Final[list[str]], instead of Final[Sequence[str]].
Why?
This test raises an Error:
Expected type 'list', got 'Sequence[str]' instead
Because of unittest.TestCase.assertListEqual, which accepts two lists.
And according to this test, changing value of kwlist breaks nothing.
What you think about this?

@TeamSpen210
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Python's test suite shouldn't be an example of valid type-checkable code. In that case perhaps the test should be loosened to assertSequenceEqual(), making the fact that it's a list an implementation detail. Or treat the test as confirming the internal details match also. In general test suites aren't really good for type checking, since they may look at internals, do dynamic things like monkeypatching and deliberately run invalid code to confirm it errors. In CPython's case, it's also ensuring that you don't get fatal errors even for the most absurd code. For the second example, it has a comment saying that they're testing an implementation detail to ensure it doesn't change, in case someone is accidentally relying on it.

@Eclips4
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Eclips4 commented Feb 5, 2023

Okay. I will change it to Final[Sequence[str]]. Thx for advices!

@AlexWaygood
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I agree with @TeamSpen210 — these are documented as "sequences" rather than "lists": https://docs.python.org/3/library/keyword.html#keyword.kwlist

Trying to alter them at runtime would likely indicate buggy assumptions in a Python program. Better to keep them typed as if they're immutable.

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keyword: Improve types of kwlist and softkwlist Eclips4/typeshed
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@TeamSpen210 @AlexWaygood @Eclips4
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