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meta-class-abc-meta (FURB180)

Preview (since v0.2.0) · Related issues · View source

Derived from the refurb linter.

Fix is always available.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for uses of metaclass=abc.ABCMeta to define abstract base classes (ABCs).

Why is this bad?

Instead of class C(metaclass=abc.ABCMeta): ..., use class C(ABC): ... to define an abstract base class. Inheriting from the ABC wrapper class is semantically identical to setting metaclass=abc.ABCMeta, but more succinct.

Example

import abc


class C(metaclass=abc.ABCMeta):
    pass

Use instead:

import abc


class C(abc.ABC):
    pass

Fix safety

The rule's fix is unsafe if the class has base classes. This is because the base classes might be validating the class's other base classes (e.g., typing.Protocol does this) or otherwise alter runtime behavior if more base classes are added.

References