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gh-129813, PEP 782: Add PyBytesWriter.overallocate - #138941
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vstinner merged 2 commits intoSep 15, 2025
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* Disable overallocation in _PyBytesWriter_CreateByteArray(). * Disable overallocation in _PyBytes_FormatEx() at the last write.
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Benchmark: python -m pyperf timeit -s 's=(b"a" * 254 + b"%s"); arg=b"b"*100' 's % (arg,)'. Result: Mean +- std dev: [ref] 165 ns +- 4 ns -> [change] 147 ns +- 1 ns: 1.12x faster. It's 18 ns faster because we avoid a realloc(). |
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@serhiy-storchaka: This change reintroduces the overallocate=0 micro-optimization in the PyBytesWriter API, but the API to disable overallocation is only available in the internal C API. |
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