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None-ness falsely assumed in loop #11430
Description
Bug Report
After foo = None, mypy thinks that foo will always be None, even if a loop can jump between the assignment and the use of foo.
To Reproduce
def main() -> None:
gonna_select = None
while True:
if gonna_select is not None:
print(1 + "lol")
gonna_select = "lol"Expected Behavior
error from 1 + "lol"
Actual Behavior
no error
Your Environment
- Mypy version used: 0.910
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.7
Activity
[-]"is not None" falsely not analyzed[/-][+]None-ness falsely assumed[/+][-]None-ness falsely assumed[/-][+]None-ness falsely assumed in loop[/+]intgr commentedon Nov 8, 2021
I think the real error should be here. Since mypy infers
gonna_selectas typeNone, why does it allow assigning a string to it?A5rocks commentedon Jan 22, 2025
Fixed by #18433