False positive for B031 in mutually exclusive branches

[janosh]

Ruff v0.0.260

# t.py
import itertools

for key, group in itertools.groupby("foobar"):
    if True:
        print(key, len(tuple(group)))
    else:
        print(key, len(tuple(group)))  # B031

ruff t.py --select B

raises false positive flake8-bugbear B031

Using the generator returned from itertools.groupby() more than once will do nothing on the second usage

[charliermarsh]

Is this incorrect? flake8-bugbear flags line 7 too.

[janosh]

If the generator uses are in mutually exclusive execution paths, I think this error should not be raised.

[charliermarsh]

Ahh yeah, I see. It might be difficult to detect this reliably.

[charliermarsh]

(But yes, it's a false positive.)

[AA-Turner]

Thank you @dhruvmanila @charliermarsh!

A