Crash at runtime

What it does

Checks for dataclass definitions with more than one field annotated with KW_ONLY.

Why is this bad?

dataclasses.KW_ONLY is a special marker used to emulate the * syntax in normal signatures. It can only be used once per dataclass.

Attempting to annotate two different fields with it will lead to a runtime error.

Examples

from dataclasses import dataclass, KW_ONLY


# Crash at runtime
@dataclass
class A:  # error
    b: int
    _1: KW_ONLY
    c: str
    _2: KW_ONLY
    d: bytes