[Python] Python typing.Literal in a guarded context

The following MWE causes mypy to error.

from typing import Literal

def expects_literal(x: Literal["foo", "bar"]) -> None:
print(f"{x=}")

def fails_mypy_check(y: str) -> None:
if y in ["foo", "bar"]:
expects_literal(y)
else:
print("format incorrect")


Results in:

mwe.py:8: error: Argument 1 to "expects_literal" has incompatible type "str"; expected "Literal['foo', 'bar']" [arg-type]


But the guard clause on line 7 ensures that y is one of the acceptable values. mypy docs call this an "exhaustiveness check" and imply it should be supported.

• typing: Literals in a non-Literal context
• mypy: Literals exhaustiveness checking

Am I missing something?

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