Incompatible types in assignment for Enum

[miketheman]

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

Using a custom enum, mypy raises an error to annotate a column

To Reproduce

import enum

from sqlalchemy import Column, Enum
from sqlalchemy.orm import declarative_base


ModelBase = declarative_base()

# also tried with:
# from sqlalchemy.orm import DeclarativeBase
# class ModelBase(DeclarativeBase):
#    ...
# Same result.


class BanReason(enum.Enum):
    AUTHENTICATION_ATTEMPTS = "authentication-attempts"


class IpAddress(ModelBase):
    ban_reason = Column(Enum(BanReason), nullable=True)


ip = IpAddress()
ip.ban_reason = BanReason.AUTHENTICATION_ATTEMPTS

reveal_type(ip.ban_reason)

Error

$ mypy repro.py
repro.py:22: error: Need type annotation for "ban_reason"  [var-annotated]
repro.py:25: error: Incompatible types in assignment (expression has type "BanReason", variable has type "Column[Any]")  [assignment]
repro.py:27: note: Revealed type is "sqlalchemy.sql.schema.Column[Any]"
Found 2 errors in 1 file (checked 1 source file)

Versions

• OS: macOS, Linux Debian bullseye
• Python: 3.11.2, 3.11.3
• SQLAlchemy: 2.016
• Type checker (eg: mypy 0.991, pyright 1.1.290, etc): mypy==1.0.1 mypy-extensions==1.0.0 mypy-zope==0.9.1

Additional context

More full-featured stack and more type-related error messages can be found on pypi/warehouse#13929 (specifically https://github.com/pypi/warehouse/actions/runs/5246828369/jobs/9476223258?pr=13929 )

I've tried adding annotations to the enum:

class BanReason(str, enum.Enum):
    AUTHENTICATION_ATTEMPTS = "authentication-attempts"

Same result.

Adding annotation directly to the Column:

class IpAddress(ModelBase):
    ban_reason: str = Column(Enum(BanReason), nullable=True)

(str could be replaced with anything here)
Error mesasage:

repro.py:22: error: Incompatible types in assignment (expression has type "Column[<nothing>]", variable has type "str")  [assignment]

[CaselIT]

Hi,

All those are expected. Mypy is supported using the new style declarative. I'm not 100% sure what's accepted by the mypy plugin, but that's deprecated.

Please see the documentation regarding the migration: https://docs.sqlalchemy.org/en/20/changelog/whatsnew_20.html#orm-declarative-models

[CaselIT]

Well the new mypy support is in the what's new document. The 1.4 style work perfectly fije in v2 but it's not supported by type checkers

[miketheman]

During the conversion to 2.0 declarative style top support the new type checking I'm hitting a confusing issue with a specific use case.

In 1.4 we use AbstractConcreteBase to create an Event, and then a mixin called HasEvents that declares __init_subclass__() to add a named subclass dynamically to the parent.
What we want is to have concrete tables for the classes mixing in (and relationships to the events).
For example, User(HasEvents) should end up with user and user_events tables, and we refer to User.Event and User.events

This example seems to be close, but not exactly, as it doesn't create an abstract class I can hook onto.

Is there some other part of the docs I'm missing on how to compose this kind of behavior in 2.0 DeclarativeBase style you can point me to?

[CaselIT]

I think that should work correctly also on 2.0. Is the issue a typing one or is it at runtime?
Do you have an example you can point to so that's clearer what you are trying to do?

[miketheman]

I'm in the middle of shipping the 2.0 upgrade with 1.4 declarative_base still intact, and will work up an example PR after it's merged that should display the issue. It might be a bit complex - I'm not entirely sure where to start carving it apart to make it a clear example.

Should that be a different Discussion, or should I rename/reshape this one?

[CaselIT]

I think a different discussion may be best