+ "description": "## What it does\nChecks for invalidly defined `NamedTuple` classes.\n\n## Why is this bad?\nAn invalidly defined `NamedTuple` class may lead to the type checker\ndrawing incorrect conclusions. It may also lead to `TypeError`s or\n`AttributeError`s at runtime.\n\n## Examples\nA class definition cannot combine `NamedTuple` with other base classes\nin multiple inheritance; doing so raises a `TypeError` at runtime. The sole\nexception to this rule is `Generic[]`, which can be used alongside `NamedTuple`\nin a class's bases list.\n\n```pycon\n>>> from typing import NamedTuple\n>>> class Foo(NamedTuple, object): ...\nTypeError: can only inherit from a NamedTuple type and Generic\n```\n\nFurther, `NamedTuple` field names cannot start with an underscore:\n\n```pycon\n>>> from typing import NamedTuple\n>>> class Foo(NamedTuple):\n... _bar: int\nValueError: Field names cannot start with an underscore: '_bar'\n```\n\n`NamedTuple` classes also have certain synthesized attributes (like `_asdict`, `_make`,\n`_replace`, etc.) that cannot be overwritten. Attempting to assign to these attributes\nwithout a type annotation will raise an `AttributeError` at runtime.\n\n```pycon\n>>> from typing import NamedTuple\n>>> class Foo(NamedTuple):\n... x: int\n... _asdict = 42\nAttributeError: Cannot overwrite NamedTuple attribute _asdict\n```",
0 commit comments