Bug: base class expression infer error

[yanyongyu]

Describe the bug

I want to create some fake class in testing to override the base class. So, ...

1. Create a dynamic class as shown in bellow.

Pylance raises two errors:

• Expected type expression but received "Type[A] | None" on var base
• Argument to class must be a base class on expression base or A

Note that if i create a var equals to base or A and then inherit it, all is OK.

To Reproduce

from typing import Optional, Type


class A:
    ...

def make_fake_class(base: Optional[Type[A]] = None):
    class FakeClass(base or A):  # Errors: Expected type expression but received "Type[A] | None"; Argument to class must be a base class
        ...
    
    Base = base or A
    
    class FakeEvent(Base):
        ...

    return FakeClass

Expected behavior

No error should be raised

Code or Screenshots

VS Code extension or command-line

• Language Server version: Pylance language server 2023.6.20 (pyright 73165c5)
• OS and version: Linux
• Python version (& distribution if applicable, e.g. Anaconda): codespaces 3.10 venv

[erictraut]

Thanks for the bug report. This will be addressed in the next release.

[erictraut]

This is included in pyright 1.1.315, which I just published. It will also be included in this week's insiders release of pylance.