"Invalid base class" raised when Base Class is a class field

Open
#3,587 8 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by running the provided reproducer with mypy and compare how the module-level Base and Types.Base are resolved when used as class bases. Trace the type-checking path for class fields and base-class validation. Done means the reproducer accepts Fails(Types.Base) without the invalid-type or invalid-base-class errors while preserving the existing reveal types.

Written by the indexing model from the issue text.

Description

needs discussion topic-inheritance

Repro:

class Foo:
    pass

Base = Foo

class Types:
    Base = Foo

reveal_type(Base)
reveal_type(Types.Base)

class Works(Base):
    pass

class Fails(Types.Base):
    pass

Results in:

test_cast.py:9: error: Revealed type is 'def () -> test_cast.Foo'
test_cast.py:10: error: Revealed type is 'def () -> test_cast.Foo'
test_cast.py:15: error: Invalid type "Base"
test_cast.py:15: error: Invalid base class

What's odd is that mypy recognizes Base and Types.Base as having identical types yet accepts Base as a base class but not Types.Base

Dominant language
Python
Stars
20.6k
Forks
3.3k
Avg merge
1d 18h
Merged PRs (30d)
54

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/mypy

All issues in python/mypy

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.