Narrowing gets lost in loops #820
Description
Describe the Bug
from typing import *
class Foo:
autogrids: None | dict[str, Any]
def f(self, xs: list[int]):
self.autogrids = {}
for a in []:
self.autogrids["test"] = True # E: ERROR 9:13-35: Cannot set item in `None`We should remember that autogrids is always going to be a dict at this point.
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