complex-assignment-in-stub (PYI017)

Derived from the flake8-pyi linter.

What it does

Checks for assignments with multiple or non-name targets in stub files.

Why is this bad?

In general, stub files should be thought of as "data files" for a type checker, and are not intended to be executed. As such, it's useful to enforce that only a subset of Python syntax is allowed in a stub file, to ensure that everything in the stub is unambiguous for the type checker.

The need to perform multi-assignment, or assignment to a non-name target, likely indicates a misunderstanding of how stub files are intended to be used.

Example

from typing import TypeAlias

a = b = int


class Klass:
    ...


Klass.X: TypeAlias = int

Use instead:

from typing import TypeAlias

a: TypeAlias = int
b: TypeAlias = int


class Klass:
    X: TypeAlias = int