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hyoinandout
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decompress_chunks reports whether the codec signalled LZMA_STREAM_END, and it short-circuits when the chunker has nothing left to feed. That early return answered "the stream ended" for the case where no input was supplied at all, so LZMADecompressor.decompress(b"") claimed a finish the decoder had never signalled. The caller latches that answer with `self.eof |= stream_end`, which only ever flips eof on. A single empty call therefore finished the object for good: needs_input went false and every later call was rejected by the `if self.eof` guard with EOFError, before a single compressed byte had been seen. CPython leaves eof false and needs_input true, and accepts compressed data handed over by a later call. d = lzma.LZMADecompressor() d.decompress(b"") # d.eof was True, now False d.decompress(blob) # was EOFError, now b'data' The zlib engine returns false from the same short-circuit; lzma had drifted away from it. bz2 was fixed incidentally by #8638 when its engine moved into crates/common, so only lzma needed a code change. Verified on macOS arm64 against CPython 3.14.7: the script from the issue now prints the documented "False True" and b'data' for both decompressors. test_decompressor_chunks_empty in Lib/test/test_lzma.py covers exactly this and no longer needs its expectedFailure marker. The added engine test is named after the zlib one that already existed and is mirrored into bz2, so all three engines stay pinned to the same behaviour. test_lzma, test_bz2, test_zlib, test_gzip, test_tarfile, cargo test --workspace, cargo fmt --check and cargo clippy -p rustpython-common --all-features --all-targets -D warnings are clean. Fixes #8637 Assisted-by: Claude Code:claude-opus-5