RUF027 false positive with reserved keywords, how to handle?

[sshishov]

Hi,

I would like to ask how to handle the cases where the "variable" for interpolation is used in the constant or other variable beforehand, example below

CONSTANT_CACHE_KEY = 'my:{id}:here'  # <-- RUF027 is triggered here (Possible f-string without an `f` prefix)

def some_function(value: str) -> None:
    cache_key = CONSTANT_CACHE_KEY.format(id=value)
    ...  # later on we use this cache key and `value` here is like a variable for cache key

I have tried to "hack" slightly by using:

CONSTANT_CACHE_KEY = f'my:{{id}}:here'  # <-- F541 is triggered here (f-string without any placeholders)

UPDATE: this is happening only with reserved keywords like id or filter. If variable does not exist, then this error is not raised.

Should it be somehow treated or handled? Or for this cases should we add # noqa: RUF027? Or maybe the good suggestion would be to rename the variable inside the string from id to object_id?

ruff version: 0.2.1

[sshishov]

Just a side note, we have updated all usages of prefix:{id}:suffix constants to prefix:{object_id}:suffix and now we do not have any issues with amazing ruff 🎉

[Avasam]

As a precision, id, filter, etc., are not reserved keywords, they are builtins (global names from the stdlib).

RUF027's heuristic detects when you try to use an existing symbols in brackets.

my_value = 5
message = "I have {my_value} things"
print(message)

But since id is always defined, it'll always trigger in your case.
It's just like https://docs.astral.sh/ruff/rules/builtin-variable-shadowing/

Maybe RUF027 could respect https://docs.astral.sh/ruff/settings/#lint_flake8-builtins_builtins-ignorelist ?

[AlexWaygood]

I think this is already fixed on main, due to:

• Ignore builtins when detecting missing f-strings #9849

It should be included in the next release!

[charliermarsh]

👍 I believe this will be fixed in the next release -- sorry about that!