[issue12165] [doc] clarify documentation of nonlocal

[Stanley]

Change by Stanley <ostanley.lee at gmail.com>:


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keywords: +patch
nosy: +slateny
nosy_count: 6.0 -> 7.0
pull_requests: +29672
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/31551

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue12165>
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