Used mypy version: 0.782
I stumbled upon some incomplete behavior related to Literal and Union. In most cases Union is not properly expanded upon conditional check when dealing with literals. Below example should describe clearly the situation.
from typing import Union
from typing_extensions import Literal
class A:
def __bool__(self) -> Literal[True]:
return True
@property
def is_ok(self) -> Literal[True]:
return True
def ok(self) -> Literal[True]:
return True
class B:
def __bool__(self) -> Literal[False]:
return False
@property
def is_ok(self) -> Literal[False]:
return False
def ok(self) -> Literal[False]:
return False
def get_a_or_b() -> Union[A, B]: ...
thing = get_a_or_b()
if thing:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
if bool(thing):
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
if thing.is_ok:
reveal_type(thing) # Revealed type is 'main.A'
else:
reveal_type(thing) # Revealed type is 'main.B'
if thing.ok():
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'I would expect that all examples will give the same result as the one with is_ok property. Maybe the bool() example would require some additional thought but it would seem wise to make it also work. Also, walrus operator makes it so that even the is_ok property example does not work. Other examples behave the same as before:
if thing := get_a_or_b():
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
if bool(thing := get_a_or_b()):
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
if (thing := get_a_or_b()).is_ok:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
if (thing := get_a_or_b()).ok():
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
else:
reveal_type(thing) # Revealed type is 'Union[main.A, main.B]'
Used mypy version:
0.782I stumbled upon some incomplete behavior related to
LiteralandUnion. In most casesUnionis not properly expanded upon conditional check when dealing with literals. Below example should describe clearly the situation.I would expect that all examples will give the same result as the one with
is_okproperty. Maybe thebool()example would require some additional thought but it would seem wise to make it also work. Also, walrus operator makes it so that even theis_okproperty example does not work. Other examples behave the same as before: