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gh-144380: Fix incorrect type check inbuffered_iternext()#144381

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fromruiyangke:fix/io/bufferedio-iternext-type-check

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@ruiyangke
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@ruiyangkeruiyangke commentedFeb 1, 2026•
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Fix incorrect type check inbuffered_iternext() that prevented the fast path from ever being taken, causing ~15% slower iteration over buffered binary files.

Sincetp is already a type object,Py_IS_TYPE(tp, X) expands toPy_TYPE(tp) == X, which compares thetype itself againstBufferedReader. This is always false, so the fast path was never taken.

pyperf benchmark:

+----------------+---------+-----------------------+| Benchmark      | buggy   | fixed                 |+================+=========+=======================+| iteration      | 3.05 ms | 2.04 ms: 1.49x faster |+----------------+---------+-----------------------+

Closes:#144380

The condition used Py_IS_TYPE(tp, ...) where tp is already a `type`,this made the fast path unreachable.
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Most changes to Pythonrequire a NEWS entry. Add one using theblurb_it web app or theblurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply theskip news label instead.

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python-cla-botbot commentedFeb 1, 2026•
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All commit authors signed the Contributor License Agreement.

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@colesbury
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Thanks for catching this. Would you please add anews entry (blurb)?

@colesburycolesbury added needs backport to 3.13bugs and security fixes needs backport to 3.14bugs and security fixes labelsFeb 1, 2026
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Fast path inbuffered_iternext is never taken due to incorrect type check

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@ruiyangke@colesbury
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