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Fix regression in container check logic (#8232) #4

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Merged
merged 1 commit into from
Jan 4, 2020
Merged

Fix regression in container check logic (#8232) #4

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2 changes: 1 addition & 1 deletion mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3915,7 +3915,7 @@ def find_isinstance_check_helper(self, node: Expression) -> Tuple[TypeMap, TypeM

# We only try and narrow away 'None' for now
if not is_optional(item_type):
pass
continue

collection_item_type = get_proper_type(builtin_item_type(collection_type))
if collection_item_type is None or is_optional(collection_item_type):
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9 changes: 9 additions & 0 deletions test-data/unit/check-optional.test
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Expand Up @@ -550,6 +550,15 @@ else:
reveal_type(b) # N: Revealed type is 'Union[__main__.A, None]'
[builtins fixtures/ops.pyi]

[case testInferInWithErasedTypes]
from typing import TypeVar, Callable

T = TypeVar('T')
def foo(f: Callable[[T], bool], it: T) -> None: ...

foo(lambda x: x in [1, 2] and bool(), 3)
[builtins fixtures/list.pyi]

[case testWarnNoReturnWorksWithStrictOptional]
# flags: --warn-no-return
def f() -> None:
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