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mypy thinks variable is None even if assigned non-None value inside loop #11900
Description
Bug Report
To Reproduce
def foo() -> None:
user = None
while True:
if user is None:
user = 123
else:
print(1 + "lol")
foo()
Expected Behavior
mypy error + runtime error
Actual Behavior
no mypy error
Your Environment
- Mypy version used: 0.930
Activity
Akuli commented on Jan 4, 2022
Workaround: user: int | None = None or user: Optional[int] = None
zhangck981 commented on Apr 2, 2022
I believe the problem might be something around the keywordis. Here are my test cases:
The first one is the case you provided:
And the second test case is:
I changed the keyword is to the operator == and it shows that mypy detects the error. Therefore, I believe the problem can be located with the keyword is.
I will continue working on this by further inspecting the source code and updating my process! However, I am new to mypy and not familiar with that. It would be best if you can provide me with some information that which files I should pay more attention to.
A5rocks commented on Jan 22, 2025
Fixed by #18433.