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Incorrect type of enum in "if" clause #20234
Description
Bug Report
mypy incorrectly calculates the type of emun if its value is checked with tuple().__contains__ in "if" clause.
To Reproduce
https://gist.github.com/mypy-play/e316d3d5b495cb113cacc9c55136dea7
Expected Behavior
main.py:10: note: Revealed type is "Literal[__main__.Op.A]"
main.py:13: note: Revealed type is "Literal[__main__.Op.B]"
Actual Behavior
main.py:10: note: Revealed type is "__main__.Op"
main.py:13: note: Revealed type is "Literal[__main__.Op.B]"
main.py:16: error: Argument 1 to "assert_never" has incompatible type "Literal[Op.A]"; expected "Never" [arg-type]
Pyright works fine with it - https://pyright-play.net/?code=JYWwDg9gTgLgBAUwHYFcQChSVnGBPMYJAc3XQGMAbAQwGda4B5MACmTQDoBRVEASgBc6OCLgBBOAF44AImozhogEJTZAIwXoAJggBmcKCiQsIYAUzCDFI4PtNwicFsw5iANFdFfcBIsQ5QCABuCNSUAPr4YAgmltbegTAoUEjxCJS2cPaS0i5KQt6iUX4BwaERUTGmfPFeicmpXum0CAWFPoQkHHQtsOFIZVCxNUA.
Your Environment
- Mypy version used: 1.18.2
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.12
Activity
sherlock2215 commentedon Nov 14, 2025
Heyy, @dimastbk can I be assigned to this issue?
I'm ready to set up the development environment and start investigating the type narrowing logic.
A5rocks commentedon Nov 15, 2025
Feel free to try, no assignment necessary.
fixed Incorrect type of enum in 'if' clause python#20234
Narrow types based on collection containment (python#20602)