contains_effect should consider f-strings to have effects because of the implicit __str__ or __repr__ call. This affects any rule that relies on contains_effect; here is an example with RUF019.
$ ruff --version
ruff 0.6.1
$ cat ruf019.py
class C:
def __init__(self):
self.i = 0
def __str__(self):
self.i += 1
return str(self.i)
if __name__ == "__main__":
c = C()
dct = {"1": "a", "2": "b"}
if f"{c}" in dct and dct[f"{c}"]:
pass
print(c.i)
$ python ruf019.py
2
$ ruff check --isolated --select RUF019 ruf019.py --fix
Found 1 error (1 fixed, 0 remaining).
$ python ruf019.py
1Some f-strings can be statically proven to not have effects, if they contain no formatted expressions (f"x") or they only format values of types formatting which is known not to have effects (f"{1}").
contains_effectshould consider f-strings to have effects because of the implicit__str__or__repr__call. This affects any rule that relies oncontains_effect; here is an example with RUF019.Some f-strings can be statically proven to not have effects, if they contain no formatted expressions (
f"x") or they only format values of types formatting which is known not to have effects (f"{1}").