[issue42536] Iterating on a zip keeps objects alive longer than expected (test_itertools leaks sometimes references)

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

Raymond Hettinger:
> If this is new, pairwise() is the most likely cause.

I reproduced the issue without involving the itertools module. It seems to be a zip_next() micro-optimization which keeps an object alive longer than epxected. This micro-optimization is not new. It's just really hard to trigger the issue.

It seems to depend if the zip object is deleted or not. The builtin zip type implements a traverse function which visits Py_VISIT(lz->result). The GC is supposed to be able to break such cycle, no?

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42536>
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