I think this is a bug, as I get inconsistent results across multiple invocations.
Depending on how I define a Type Alias, it can or can not be used as a valid type in another file - on every other invocation of mypy.
from typing import Literal
from typing import Optional
from typing import Union
TYPE_FOO = Optional[str]
TYPE_BAR = Union[str, None]
def biz(a: TYPE_FOO, b: TYPE_BAR) -> Literal[True]:
return True
However, if the type aliases are split into another file, TYPE_FOO (using Optional) is sometimes invalid in mypy and triggers "Variable "TYPE_FOO" is not valid as a type [valid-type]" – while the functionally equivalent TYPE_BAR (using Union) is always valid. The error from Optional seems to appear on every-other invocation of mypy. I can't seem to recreate the error reliably with the small test case alone, but dropping it into larger projects seems to trigger it on every-other run.
To Reproduce
custom_types.py
from typing import Optional
from typing import Union
TYPE_FOO = Optional[str]
TYPE_BAR = Union[str, None]
project.py
from typing import Literal
from .custom_types import TYPE_FOO
from .custom_types import TYPE_BAR
def biz(a: TYPE_FOO, b: TYPE_BAR) -> Literal[True]:
return True
Expected Behavior
I expected no errors for either usage.
I expected consistent behavior from mypy across runs when it thinks there is an issue.
Actual Behavior
MyPy alternates an error for the imported type that uses Optional on every-other run:
Variable "TYPE_FOO" is not valid as a type [valid-type]
i.e. The first run has no errors, the second has the error, the third has no errors, the fourth has the error, etc
The type using Union never triggers an error.
Your Environment
Mypy version used:
1.10
Mypy command-line flags:
NA
Mypy configuration options from mypy.ini (and other config files):
check_untyped_defs = True
Bug Report
I think this is a bug, as I get inconsistent results across multiple invocations.
Depending on how I define a Type Alias, it can or can not be used as a valid type in another file - on every other invocation of mypy.
However, if the type aliases are split into another file,
TYPE_FOO
(usingOptional
) is sometimes invalid in mypy and triggers "Variable "TYPE_FOO" is not valid as a type [valid-type]" – while the functionally equivalentTYPE_BAR
(usingUnion
) is always valid. The error fromOptional
seems to appear on every-other invocation of mypy. I can't seem to recreate the error reliably with the small test case alone, but dropping it into larger projects seems to trigger it on every-other run.To Reproduce
custom_types.py
project.py
Expected Behavior
I expected no errors for either usage. I expected consistent behavior from mypy across runs when it thinks there is an issue.
Actual Behavior
MyPy alternates an error for the imported type that uses
Optional
on every-other run:i.e. The first run has no errors, the second has the error, the third has no errors, the fourth has the error, etc
The type using
Union
never triggers an error.Your Environment
mypy.ini
(and other config files): check_untyped_defs = True