Unhelpful error "Invalid base class mypy(error)"

[vivaldus]

The following sql-entity class was generated by sqlalchemy -- so this is the standard way to create such a class and operate it. However, mypy calls Base here an Invalid base class. But why? No further details are given, I see no such error described in mypy documentation, and googling "Invalid base class" doesn't lead me to any obvious results. I have no way to diagnose the problem.

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class SomeClass(Base)
    ....

mypy version 0.660
python version 3.7.2

[emmatyping]

In this case it is because the Base class is dynamic (computed from a function return), therefore mypy cannot use it for static analysis.

Also this is a duplicate of #2477 (the issue is tracking a better error message and add support for dynamic base classes #2477 (comment)).

[ilevkivskyi]

@vivaldus As I mentioned in my closing notice for #2477 you should use SQLAlchemy plugin. The error message is now tracked in #4030.