https://github.com/python/cpython/commit/bac4edad69bb20dd9460766e062637cae999e1e0
commit: bac4edad69bb20dd9460766e062637cae999e1e0
branch: main
author: Gregory P. Smith <[email protected]>
committer: gpshead <[email protected]>
date: 2024-06-16T22:47:10-07:00
summary:
gh-112346: Document the OS byte in `gzip.compress` output change in 3.11
(#120480)
gh-112346: Describe the "os" byte in gzip output change.
files:
M Doc/library/gzip.rst
M Doc/whatsnew/3.11.rst
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index 152cba4f653cb4..6b6e158f6eba2c 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -196,7 +196,9 @@ The module defines the following items:
.. versionchanged:: 3.11
Speed is improved by compressing all data at once instead of in a
streamed fashion. Calls with *mtime* set to ``0`` are delegated to
- :func:`zlib.compress` for better speed.
+ :func:`zlib.compress` for better speed. In this situation the
+ output may contain a gzip header "OS" byte value other than 255
+ "unknown" as supplied by the underlying zlib implementation.
.. versionchanged:: 3.13
The gzip header OS byte is guaranteed to be set to 255 when this function
diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 7a74df330a86c7..b601bd453f5be5 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -768,6 +768,21 @@ functools
(Contributed by Yurii Karabas in :issue:`46014`.)
+.. _whatsnew311-gzip:
+
+gzip
+----
+
+* The :func:`gzip.compress` function is now faster when used with the
+ **mtime=0** argument as it delegates the compression entirely to a single
+ :func:`zlib.compress` operation. There is one side effect of this change: The
+ gzip file header contains an "OS" byte in its header. That was traditionally
+ always set to a value of 255 representing "unknown" by the :mod:`gzip`
+ module. Now, when using :func:`~gzip.compress` with **mtime=0**, it may be
+ set to a different value by the underlying zlib C library Python was linked
+ against.
+ (See :gh:`112346` for details on the side effect.)
+
.. _whatsnew311-hashlib:
hashlib
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