Incorrect type of enum in "if" clause

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

@dimastbk

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.

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)

Navigation Menu

Repository navigation

Incorrect type of enum in "if" clause #20234

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Incorrect type of enum in "if" clause #20234

Description

Activity

sherlock2215 commented on Nov 14, 2025

A5rocks commented on Nov 15, 2025

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions