Invalid base class "Base" when returned by a function

Describe the bug mypy returns [Invald ](error: Invalid base class “Base” [misc]) when Base class is returned by a function.

To Reproduce

pip install sqlalchemy[mypy]==1.4.44
mypy --config-file=mypy.ini test.py

mypy.ini

[mypy]
plugins = sqlalchemy.ext.mypy.plugin

test.py

from sqlalchemy import String, select
from sqlalchemy.orm import declarative_base
from typing import Optional, Dict, Type
import sqlalchemy
from sqlalchemy.orm.ext import DeclarativeMeta

def get_base() -> Type[DeclarativeMeta]:
    return declarative_base()

Base: Type[DeclarativeMeta] = get_base()

class User(Base):
    __tablename__ = "user"

    id = sqlalchemy.Column(sqlalchemy.Integer, primary_key=True)
    name = sqlalchemy.Column(sqlalchemy.String)

Error

error: Invalid base class "Base"

Versions.

• OS: Ubuntu 22.04
• Python: 3.8
• SQLAlchemy: 1.4.44
• mypy: 0.991
• SQLAlchemy2-stubs: 0.0.2a29

Have a nice day!

[zzzeek]

short answer no, there’s nothing different. as long as your Base class is making mappings, it’s doing the thing it’s supposed to do.

[zzzeek]

the declarative_base() function invokes Python code that is the equivalent operation as doing your “class Base” declaration. It uses the Python type() function to create a new type. But also it could just as well have that same “class Base” declaration inside of it, then return the class; Python typing has no way to represent that returned class as something you can subclass.