I see why Ruff did not enable W by default. All but one of the checks (invalid escape sequences) are handled by black --check or an E lint on line length, so it is pretty redundant.

• https://beta.ruff.rs/docs/rules/#warning-w

Since Python 3.6, a DeprecationWarning is emitted for invalid escape sequences:

$ python3 -W default -c 'print(list("\z"))'
<string>:1: DeprecationWarning: invalid escape sequence '\z'
['\\', 'z']

This will be caught by pytest's treat-warnings-as-errors setting:

filterwarnings = [
   "error",
]

Moreover, Python 3.12 will be upgrading invalid escape sequences to an (on by default) SyntaxWarning , so perhaps we can simply defer this setting entirely to keep the Ruff configuration simpler:

• https://docs.python.org/3.12/whatsnew/3.12.html#other-language-changes

A backslash-character pair that is not a valid escape sequence now generates a SyntaxWarning, instead of DeprecationWarning. For example, re.compile("\d+.\d+") now emits a SyntaxWarning ("\d" is an invalid escape sequence), use raw strings for regular expression: re.compile(r"\d+.\d+"). In a future Python version, SyntaxError will eventually be raised, instead of SyntaxWarning. (Contributed by Victor Stinner in gh-98401.)

That's a good point. I got bit by invalid-escape-sequence and did not think about the others in the context of Black. I concur that this is not actually something worth turning on.