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Add narrowing Union w/ bool Literal via identity check #8821

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Merged
merged 3 commits into from
May 19, 2020
Merged

Add narrowing Union w/ bool Literal via identity check #8821

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56da848
Add narrowing Union with boolean Literal with identity check
sbdchd May 14, 2020
75e0cf9
fix formatting for long line
sbdchd May 14, 2020
c6f3006
update comment, add another test case
sbdchd May 14, 2020
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6 changes: 4 additions & 2 deletions mypy/typeops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -604,10 +604,12 @@ def is_singleton_type(typ: Type) -> bool:
constructing two distinct instances of 100001.
"""
typ = get_proper_type(typ)
# TODO: Also make this return True if the type is a bool LiteralType.
# TODO:
# Also make this return True if the type corresponds to ... (ellipsis) or NotImplemented?
return (
isinstance(typ, NoneType) or (isinstance(typ, LiteralType) and typ.is_enum_literal())
isinstance(typ, NoneType)
or (isinstance(typ, LiteralType)
and (typ.is_enum_literal() or isinstance(typ.value, bool)))
or (isinstance(typ, Instance) and typ.type.is_enum and len(get_enum_values(typ)) == 1)
)

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42 changes: 42 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -984,3 +984,45 @@ if true_or_false:
else:
reveal_type(true_or_false) # N: Revealed type is 'Literal[False]'
[builtins fixtures/primitives.pyi]

[case testNarrowingLiteralIdentityCheck]
from typing import Union
from typing_extensions import Literal

str_or_false: Union[Literal[False], str]

if str_or_false is not False:
reveal_type(str_or_false) # N: Revealed type is 'builtins.str'
else:
reveal_type(str_or_false) # N: Revealed type is 'Literal[False]'

if str_or_false is False:
reveal_type(str_or_false) # N: Revealed type is 'Literal[False]'
else:
reveal_type(str_or_false) # N: Revealed type is 'builtins.str'

str_or_true: Union[Literal[True], str]

if str_or_true is True:
reveal_type(str_or_true) # N: Revealed type is 'Literal[True]'
else:
reveal_type(str_or_true) # N: Revealed type is 'builtins.str'

if str_or_true is not True:
reveal_type(str_or_true) # N: Revealed type is 'builtins.str'
else:
reveal_type(str_or_true) # N: Revealed type is 'Literal[True]'

str_or_bool_literal: Union[Literal[False], Literal[True], str]

if str_or_bool_literal is not True:
reveal_type(str_or_bool_literal) # N: Revealed type is 'Union[Literal[False], builtins.str]'
else:
reveal_type(str_or_bool_literal) # N: Revealed type is 'Literal[True]'

if str_or_bool_literal is not True and str_or_bool_literal is not False:
reveal_type(str_or_bool_literal) # N: Revealed type is 'builtins.str'
else:
reveal_type(str_or_bool_literal) # N: Revealed type is 'Union[Literal[False], Literal[True]]'

[builtins fixtures/primitives.pyi]