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Pattern matching is not exhaustive in a weird edge case with an enum member subject #18875
Closed as duplicate
Description
Bug Report
- Access an enum member by name, but the name cannot be inline (e.g. you can access it from a variable)
- Directly use the enum member as the subject in a match statement
If you do this, mypy does not think the match statement is exhaustive.
To Reproduce
https://mypy-play.net/?mypy=latest&python=3.13&flags=strict&gist=0d11136907ace743b0f2412ad0f26bb1
from enum import Enum, auto
from typing import reveal_type
class Thing(Enum):
ONE = auto()
TWO = auto()
two = "TWO"
def good() -> int:
version = Thing[two]
match version:
case Thing.ONE:
return 1
case Thing.TWO:
return 2
def bad() -> int:
match Thing[two]:
case Thing.ONE:
return 1
case Thing.TWO:
return 2
case _ as thing:
reveal_type(thing)If you replace Thing[two] with Thing["TWO"], the problem also goes away.
Expected Behavior
Both match statements are exhaustive, so there is a return statement for all cases.
Actual Behavior
main.py:22: error: Missing return statement [return]
main.py:29: note: Revealed type is "__main__.Thing"
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.15.0
- Mypy command-line flags: --strict
- Python version used: 3.13
Activity
[-]Pattern matching is not exhaustive if enum member subject is accessed by name and the name is in a variable[/-][+]Pattern matching is not exhaustive in a weird edge case with an enum member subject[/+]sterliakov commentedon Apr 4, 2025
Given that your
goodversion works, is it the same as #18440? Currently we do not narrow types of complex expressions inmatchstatement other than function calls.injust commentedon Apr 4, 2025
Yes, it seems like the same issue. In the repro for #18440, if you change the function
bfromto
Then it type checks. This is the same behaviour that I'm seeing here.