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[3.12] gh-112346: Document the OS byte in gzip.compress
output change in 3.11 (GH-120480) (#120613)
gh-112346: Document the OS byte in `gzip.compress` output change in 3.11 (GH-120480)
(cherry picked from commit bac4edad69
)
gh-112346: Describe the "os" byte in gzip output change.
Co-authored-by: Gregory P. Smith <greg@krypto.org>
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@ -194,7 +194,9 @@ The module defines the following items:
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.. versionchanged:: 3.11
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.. versionchanged:: 3.11
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Speed is improved by compressing all data at once instead of in a
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Speed is improved by compressing all data at once instead of in a
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streamed fashion. Calls with *mtime* set to ``0`` are delegated to
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streamed fashion. Calls with *mtime* set to ``0`` are delegated to
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:func:`zlib.compress` for better speed.
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:func:`zlib.compress` for better speed. In this situation the
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output may contain a gzip header "OS" byte value other than 255
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"unknown" as supplied by the underlying zlib implementation.
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.. function:: decompress(data)
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.. function:: decompress(data)
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@ -768,6 +768,21 @@ functools
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(Contributed by Yurii Karabas in :issue:`46014`.)
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(Contributed by Yurii Karabas in :issue:`46014`.)
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.. _whatsnew311-gzip:
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gzip
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----
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* The :func:`gzip.compress` function is now faster when used with the
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**mtime=0** argument as it delegates the compression entirely to a single
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:func:`zlib.compress` operation. There is one side effect of this change: The
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gzip file header contains an "OS" byte in its header. That was traditionally
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always set to a value of 255 representing "unknown" by the :mod:`gzip`
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module. Now, when using :func:`~gzip.compress` with **mtime=0**, it may be
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set to a different value by the underlying zlib C library Python was linked
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against.
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(See :gh:`112346` for details on the side effect.)
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.. _whatsnew311-hashlib:
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.. _whatsnew311-hashlib:
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hashlib
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hashlib
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