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PEP 572: Type not narrowed correctly in assignment #7316
Description
Example from @gvanrossum in #6899:
from typing import Optional
class C:
def foo(self):
pass
def good(b: Optional[C]) -> None:
a = b
if a:
a.foo()
def bad(b: Optional[C]) -> None:
if a := b:
a.foo() # E: Item "None" of "Optional[C]" has no attribute "foo"
Activity
ilevkivskyi commentedon Nov 22, 2019
This is actually pretty important to support, this example:
is the flagship example taken from Python 3.8 What's New, and is actually the prime use case for assignment expressions in general. Raising priority to high.
Narrow types for walrus assignment in if statements
Narrow types for walrus assignment in if statements (#8258)
📇 Add type hints to all the code