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gzip.decompress(), bz2.decompress(), lzma.decompress() and compression.zstd.decompress() passed all of the remaining input to a new decompressor for every member and copied the rest back via unused_data. Feed each member in chunks of increasing size instead.
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needs backport to 3.14
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October 22, 2026 18:57
gpshead
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Oct 22, 2026
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A high level comment I have on this PR... could or should we meaningfully factor out the common shape memoryview loop code used across multiple decompressors?
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I think yes, seems reasonable for |
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The one-shot
decompress()functions ofgzip,bz2,lzmaandcompression.zstdgave each new decompressor all of the remaining input and copied the rest back throughunused_data, so input with many members took quadratic time. They now feed each member in chunks that start at 1 KiB and double, and step back overunused_databy offset; the first chunk is the whole input, so single-member data still takes one decompressor call. Results are unchanged for bytes-like input, butbz2,lzmaandzstdnow slice amemoryviewof the argument, so a non-contiguousmemoryviewraisesTypeErrorwhere it raisedBufferError, and theTypeErrorfor a non-buffer argument has a different message.Fixes #160310
ANT-2026-9R8SO5S2
decompress()ingzip,bz2,lzmaandcompression.zstdis quadratic in the number of members #160310