Confusing error message when using AnyStr

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#963 6 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
developer-experience, devtools

Research direction

Reproduce the example in a small Python file and trace the type-checking path that emits Type argument 1 of "f" has incompatible value "object". Improve the diagnostic so the mixed str/bytes arguments and AnyStr constraint are understandable, then verify the example reports the clearer message.

Written by the indexing model from the issue text.

Description

bug priority-0-high topic-join-v-union topic-usability 
from typing import AnyStr

def f(x: AnyStr, y: AnyStr) -> AnyStr:
    print(x + y)

f('one', b'two')

This correctly fails to typecheck because the second arg is bytes, but the error message is hard to follow:

test.py:6: error: Type argument 1 of "f" has incompatible value "object"
Dominant language
Python
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Avg merge
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Merged PRs (30d)
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