gh-142732: Prevent reentrancy in itertools.zip_longest#150675
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brijkapadia wants to merge 5 commits into
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gh-142732: Prevent reentrancy in itertools.zip_longest#150675brijkapadia wants to merge 5 commits into
itertools.zip_longest#150675brijkapadia wants to merge 5 commits into
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Adds a check in `functools.zip_longest` that raises a `ValueError` when a reentrancy is detected.
brijkapadia
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functools.zip_longestitertools.zip_longest
eendebakpt
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May 31, 2026
| return NULL; | ||
| if (lz->numactive == 0) | ||
| if (lz->running == 1) { | ||
| PyErr_SetString(PyExc_ValueError, |
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itertools.tee raises a RuntimeError, but generators raise a ValueError on re-entrant calls. In #150589 I picked RuntimeError for pairwise re-entrant calls.
I have no strong opinion on the type of error, but lets make it an informed decision and then be consistent. @rhettinger
eendebakpt
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May 31, 2026
| @@ -0,0 +1 @@ | |||
| Now :func:`itertools.zip_longest` raises an :exc:`ValueError` when a reentrancy is detected. | |||
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This is a behaviour change. I think we should add an entry to the 3.16 whatsnew (https://docs.python.org/3.16/whatsnew/3.16.html). Can be done in a follow PR once we know which other iterators are changed.
eendebakpt
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May 31, 2026
eendebakpt
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May 31, 2026
Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
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Adds a check in
itertools.zip_longestthat raises aValueErrorwhen a reentrancy is detected.itertools.zip_longest_next/islice/batchedvia re-entrant iterator #142732