If a with statement’s target is a global variable that was assigned before, a false “redefinition of unused variable” is reported.

[manueljacob]

from contextlib import nullcontext

def f():
    global glob
    glob = 0
    assert g() == 0
    with nullcontext(enter_result=1) as glob:
        assert g() == 1

def g():
    return glob

With ruff 0.7.3:

test.py:8:41: F811 Redefinition of unused `glob` from line 6
  |
6 |     glob = 0
7 |     assert g() == 0
8 |     with nullcontext(enter_result=1) as glob:
  |                                         ^^^^ F811
9 |         assert g() == 1
  |
  = help: Remove definition: `glob`

Found 1 error.

However, glob is used by g(), so neither of the assignments can be removed.

I’m aware that according to the Python documentation, “names listed in a global statement must not be defined as formal parameters, or as targets in with statements or except clauses, or in a for target list, class definition, function definition, import statement, or variable annotation”. However, that is currently not enforced by CPython or PyPy. There could be a ruff rule that reports an error in this case, but that’s a separate issue.

[MichaReiser]

@AlexWaygood would you mind taking a look at this issue?