8000 Fix make_simplified_union for instances with last_known_value by freundTech · Pull Request #10373 · python/mypy · GitHub
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Fix make_simplified_union for instances with last_known_value #10373

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Merged
merged 1 commit into from
Apr 30, 2021
Merged

Fix make_simplified_union for instances with last_known_value #10373

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14 changes: 13 additions & 1 deletion mypy/typeops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -367,7 +367,8 @@ def make_simplified_union(items: Sequence[Type],
# Keep track of the truishness info for deleted subtypes which can be relevant
cbt = cbf = False
for j, tj in enumerate(items):
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased) and \
is_redundant_literal_instance(ti, tj):
# We found a redundant item in the union.
removed.add(j)
cbt = cbt or tj.can_be_true
Expand Down Expand Up @@ -805,3 +806,14 @@ def custom_special_method(typ: Type, name: str, check_all: bool = False) -> bool
return True
# TODO: support other types (see ExpressionChecker.has_member())?
return False


def is_redundant_literal_instance(general: ProperType, specific: ProperType) -> bool:
if not isinstance(general, Instance) or general.last_known_value is None:
return True
if isinstance(specific, Instance) and specific.last_known_value == general.last_known_value:
return True
if isinstance(specific, UninhabitedType):
return True

return False
2 changes: 1 addition & 1 deletion test-data/unit/check-python38.test
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Expand Up @@ -268,7 +268,7 @@ def f(x: int = (c := 4)) -> int:
f(x=(y7 := 3))
reveal_type(y7) # N: Revealed type is "builtins.int"

reveal_type((lambda: (y8 := 3) and y8)()) # N: Revealed type is "Literal[3]?"
reveal_type((lambda: (y8 := 3) and y8)()) # N: Revealed type is "builtins.int"
y8 # E: Name "y8" is not defined

y7 = 1.0 # E: Incompatible types in assignment (expression has type "float", variable has type "int")
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