B023 potential false positive (with shadowed variable names)

[XN137]

python code:

lambdas = []
for val in range(3):
    lambdas.append(lambda val=val: print(val))

for lam in lambdas:
    lam()

funcs = []
for val in range(3):
    def make_func(val):
        def tmp():
            return print(val)

        return tmp


    funcs.append(make_func(val))

for func in funcs:
    func()

funcs = []
for val in range(3):
    def make_func(val=val):
        def tmp():
            return print(val)

        return tmp


    funcs.append(make_func())

for func in funcs:
    func()

outputs:

0
1
2
0
1
2
0
1
2

but ruff 0.0.263 reports B023 violations for the make_func variants (because the val variable is shadowed):

falsepositive.py:
  12:26 B023 Function definition does not bind loop variable `val`

  26:26 B023 Function definition does not bind loop variable `val`

note that the last make_func variant might be a common pattern in python codebases, see https://stackoverflow.com/a/3431699

[charliermarsh]

Agree, does look like a bug. We probably don't have proper scope tracking there.

[XN137]

just to confirm: after upgrading to 0.0.264 we could enable B023 across our codebase without violations, thanks a lot for the quick fix!