Rule suggestion: prefer tuples over lists when used inline

[njourdane]

This suggestion is based on this discussion, where I learned that since tuples are immutable, it helps type checkers to infer more precise types:

from typing import Literal
from typing_extensions import LiteralString

def foo1(bar: LiteralString) -> Literal["a", "b", "c"]:
    return bar if bar in ("a", "b") else "c" # good

def foo2(bar: LiteralString) -> Literal["a", "b", "c"]:
    return bar if bar in ["a", "b"] else "c" # type error on ty and pyright

Personally, I would prefer the first solution from now on.

Does this rule makes sense for you?

[ntBre]

Hmm, that's interesting, thanks!

We have a closely related rule in literal-membership (PLR6201), but it recommends a set literal in both the list and tuple cases here, which also sounds like it wouldn't help type checkers. We'd have to figure out how to resolve that conflict before we could add a rule suggesting a tuple instead.