F821 false positive: dict.__dict__['fromkeys']

[AA-Turner]

Ruff doesn't like classmethod descriptors, or seems to think that they're undefined, which is rather odd.

a = type({}).__dict__['fromkeys']
b = dict.__dict__['fromkeys']
assert a is b

Saving the above to bug.py, and running only with F821:

PS I:\Development> ruff -V
ruff 0.1.9
PS I:\Development> ruff --isolated --show-source --select F821 bug.py
bug.py:2:20: F821 Undefined name `fromkeys`
  |
1 | a = type({}).__dict__['fromkeys']
2 | b = dict.__dict__['fromkeys']
  |                    ^^^^^^^^ F821
3 | assert a is b
  |

Found 1 error.

Note only the second line yields an error -- using type({}) as an indirection for dict solves the issue.

A

[charliermarsh]

Thanks — I’m guessing it thinks it’s a type annotation, as when subscripting dict directly.

[charliermarsh]

Closed by #9309.

[AA-Turner]

Thanks Charlie!

A