Incorrect inferred type of returned value of Callable that has a generic Optional return type
#1462
Comments
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Thanks for the bug report. There is logic in the type evaluator that handles a union return type that includes both concrete types and one or more generic types that are not "solved" when the call expression is evaluated. This is important in cases like this: def func(a: List[int | T]) -> int | T:
...
reveal_type(func(["hi"])) # int | str
# In this case, "T" remains unsolved, and we don't want the resulting
# type to be `int | T` because `T` has no meaning outside of the scope
# of the callee. For that reason, the `T` is dropped from the resulting type.
reveal_type(func([3])) # intThis logic resulted in the type of However, in this example, This will be fixed in the next release. |
erictraut
added
bug
|
This issue has been fixed in version 2021.6.3, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#202163-23-june-2021 |
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I'm afraid the bug is still not solved completely. The code that originally produced the bug is a little more complex than the sample I provided here. This other sample produces the same effect: from typing import Optional, TypeVar
from collections.abc import Callable
T = TypeVar("T")
U = TypeVar("U")
def h(x: T, f: Callable[[T], Optional[U]]) -> U:
def g() -> U:
y = f(x)
if y is not None:
return y
raise ValueError()
return g() |
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Yep, my previous fix didn't account for nested scopes. I've updated it to handle that case as well. |
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Many thanks for your rapidity! Also, I have encountered another problem that might be related to this bug but I'm not totally sure. I was waiting for today's release to see if it would fix it but apparently it didn't. Let me know if you think I should open another issue. The snippet is this: from typing import (
Any,
Callable,
Optional,
TypeVar,
Union,
)
T = TypeVar("T")
U = TypeVar("U")
def g(f: Callable[[Any], Optional[T]]) -> T:
...
def h(t1: type[T], t2: type[U]) -> Union[T, U]:
def f(x: Any) -> Union[T, U]:
if isinstance(x, (t1, t2)):
return x
raise ValueError()
x = g(f)
return xThe type of |
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Please file a new issue in the pyright repo, and I'll take a look at it. On first inspection, mypy also evaluates the type as |
Environment data
Expected behaviour
The infered type of
yshoud beU | None.Actual behaviour
The inferred type of the local variable
yin the function listed below isNone. Because of this, whithin theif y is not None:the inferred type becomesNeverand if I returnyPyLance marks it as an error.Logs
Code Snippet / Additional information
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