Asynchronous sessionmaker initialization type error

Describe the bug mypy fails on asynchronous sessionmaker initialization.

Expected behavior No errors.

To Reproduce Please try to provide a Minimal, Complete, and Verifiable example. See also Reporting Bugs on the website, and some example issues.

Please do not use Flask-SQLAlchemy or any other third-party extensions or dependencies in test cases. The test case must illustrate the problem without using any third party SQLAlchemy extensions. Otherwise, please report the bug to those projects first.

import os

from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.ext.asyncio import create_async_engine
from sqlalchemy.orm import sessionmaker

engine = create_async_engine(os.getenv("DATABASE_URL"))
async_session = sessionmaker(engine, class_=AsyncSession)

Error

session.py:8: error: Value of type variable "_TSessionMakerType" of "sessionmaker" cannot be "AsyncSession"
Found 1 error in 1 file (checked 1 source file)

Versions.

• OS: Linux
• Python: 3.9.6
• SQLAlchemy: 1.4.23
• mypy: 0.910
• SQLAlchemy2-stubs: v0.0.2a9

Additional context The problem appeared on the latest release of sqlalchemy2-stubs and was not present on v0.0.2a8.

Have a nice day!

[zzzeek]

@mjpieters I am hoping 2.0 betas are very soon. that’s where these issues if you have them will be permanently fixed so i hope you have time to test a bit.

[mjpieters]

This appears to have regressed? I’m using version 0.0.2a27, and the example in this issue now produces:

Argument of type "Type[AsyncSession]" cannot be assigned to parameter "class_" of type "Type[_TSessionMakerType@sessionmaker]" in function "__init__"
  Type "Type[AsyncSession]" cannot be assigned to type "Type[_TSessionMakerType@sessionmaker]"

when using Pyright.

I noticed that almost the same error message appears when using sqlalchemy.create_engine() and sqlalchemy.orm.Session:

Argument of type "Type[Session]" cannot be assigned to parameter "class_" of type "Type[_TSessionMakerType@sessionmaker]" in function "__init__"
  Type "Type[Session]" cannot be assigned to type "Type[_TSessionMakerType@sessionmaker]"