Mapped property is interpreted to mapped type instead of InstrumentedAttibute on union

[Fred-si]

Ensure stubs packages are not installed

• No sqlalchemy stub packages is installed (both sqlalchemy-stubs and sqlalchemy2-stubs are not compatible with v2)

Verify if the api is typed

• The api is not in a module listed in #6810 so it should pass type checking

Describe the typing issue

When I have a variable that contain an union of model type (foo: type[ModelA | ModelB]) property type is interpreted by mypy as mapped_type instead of InstrumentedAttribute[mapped_type].

To Reproduce

from typing_extensions import reveal_type

from sqlalchemy.orm import DeclarativeBase, Mapped


class Foo(DeclarativeBase):
    foobar: Mapped[str]


class Bar(DeclarativeBase):
    foobar: Mapped[str]


def foo(attribute: InstrumentedAttribute[Any]) -> None:
    pass


union: type[Foo | Bar] = Foo
foo(union.foobar)

Error

main.py:21: error: Argument 1 to "foo" has incompatible type "str"; expected "InstrumentedAttribute[Any]"  [arg-type]

Versions

• OS: Ubuntu 20.04
• Python: 3.10.12 | 3.11.6 | 3.12.0
• SQLAlchemy: 2.0.22 | 2.0.23
• Type checker (eg: mypy 0.991, pyright 1.1.290, etc): mypy 1.7.1

Additional context

sqlalchemy and mypy are installed in venv

requirements.txt

SQLAlchemy==2.0.23
mypy==1.7.1

minimal example can be found here https://github.com/Fred-si/sqlalchemy_union_type_issue

[zzzeek]

that's going to be a Mypy issue. If you replace InstrumentedAttribute with a plain Python descriptor you will likely get the same result.

I'll show you a confirming case in a few (will close this issue).

[zzzeek]

adding reveal_type() to your example, here's mypy:

$ mypy test3.py 
lib/sqlalchemy/util/concurrency.py:84: error: Cannot find implementation or library stub for module named "greenlet"  [import-not-found]
lib/sqlalchemy/util/concurrency.py:84: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
test3.py:19: note: Revealed type is "builtins.str"
test3.py:21: error: Argument 1 to "foo" has incompatible type "str"; expected "InstrumentedAttribute[Any]"  [arg-type]
Found 2 errors in 2 files (checked 1 source file)

however here's pyright

$ pyright test3.py 
/home/classic/dev/sqlalchemy/test3.py
  /home/classic/dev/sqlalchemy/test3.py:19:13 - information: Type of "union.foobar" is "InstrumentedAttribute[str]"
0 errors, 0 warnings, 1 information 

pyright is correct, mypy is wrong. mypy has a lot of problems dealing with Type objects in a meaningful way.

Here's a non-SQLAlchemy example, feel free to report this to mypy:

from __future__ import annotations

from typing import Any, overload, Generic, TypeVar, Optional, Union

_T_co = TypeVar("_T_co", bound=Any, covariant=True)


class InstrumentedAttribute(Generic[_T_co]):
    @overload
    def __get__(
        self, instance: None, owner: Any
    ) -> InstrumentedAttribute[_T_co]:
        ...

    @overload
    def __get__(self, instance: object, owner: Any) -> _T_co:
        ...

    def __get__(
        self, instance: Optional[object], owner: Any
    ) -> Union[InstrumentedAttribute[_T_co], _T_co]:
        ...

    def __set__(self, instance: Any, value: Any) -> None:
        ...

    def __delete__(self, instance: Any) -> None:
        ...


class Foo:
    foobar: InstrumentedAttribute[str]


class Bar:
    foobar: InstrumentedAttribute[str]


def foo(attribute: InstrumentedAttribute[Any]) -> None:
    pass


union: type[Foo | Bar] = Foo

reveal_type(union.foobar)

foo(union.foobar)

reproduces in the same way as the previous example for both tools (correct for pyright, wrong for mypy)

[CaselIT]

This is issue python/mypy#5570 of mypy

Considering it's open since 2018 I'm not sure how soon it will be fixed

[Fred-si]

Thanks for yours replies. My apologies for the mistake.

[CaselIT]

No problem!

[md384]

This will hopefully be fixed by python/mypy#16604

[CaselIT]

thanks for reporting back. No change is required in sqlalchemy, correct?

[md384]

thanks for reporting back. No change is required in sqlalchemy, correct?

Correct - it appears to be a bug only in mypy.