Mar 19, 2025
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
 The module defines the following items:


 .. function:: open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)
 .. function:: open(filename, mode='rb', compresslevel=6, encoding=None, errors=None, newline=None)

   Open a gzip-compressed file in binary or text mode, returning a :term:`file
   object`.

   .. versionadded:: 3.8

 .. class:: GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None)
 .. class:: GzipFile(filename=None, mode=None, compresslevel=6, fileobj=None, mtime=None)

   Constructor for the :class:`GzipFile` class, which simulates most of the
   methods of a :term:`file object`, with the exception of the :meth:`~io.IOBase.truncate`
      attribute instead.


 .. function:: compress(data, compresslevel=9, *, mtime=0)
 .. function:: compress(data, compresslevel=6, *, mtime=0)

   Compress the *data*, returning a :class:`bytes` object containing
   the compressed data.  *compresslevel* and *mtime* have the same meaning as in
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
        return cls(name, mode, fileobj, **kwargs)

    @classmethod
    def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
    def gzopen(cls, name, mode="r", fileobj=None, compresslevel=6, **kwargs):
        """Open gzip compressed tar archive name for reading or writing.
           Appending is not allowed.
        """
        return t

    @classmethod
    def bz2open(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
    def bz2open(cls, name, mode="r", fileobj=None, compresslevel=6, **kwargs):
        """Open bzip2 compressed tar archive name for reading or writing.
           Appending is not allowed.
        """
diff --git a/Misc/NEWS.d/next/Library/2025-03-19-12-41-42.gh-issue-91349.8eTOCP.rst b/Misc/NEWS.d/next/Library/2025-03-19-12-41-42.gh-issue-91349.8eTOCP.rst
 Adjust default compression level to 6 (down from 9) in gzip and tarfile.
 It is the default level used by most compression tools and a better
 tradeoff between speed and performance.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -26,7 +26,7 @@ Note that additional file formats which can be decompressed by the
		The module defines the following items:


		.. function:: open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)
		.. function:: open(filename, mode='rb', compresslevel=6, encoding=None, errors=None, newline=None)

		Open a gzip-compressed file in binary or text mode, returning a :term:`file
		object`.
Expand DownExpand Up		@@ -67,7 +67,7 @@ The module defines the following items:

		.. versionadded:: 3.8

		.. class:: GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None)
		.. class:: GzipFile(filename=None, mode=None, compresslevel=6, fileobj=None, mtime=None)

		Constructor for the :class:`GzipFile` class, which simulates most of the
		methods of a :term:`file object`, with the exception of the :meth:`~io.IOBase.truncate`
Expand DownExpand Up		@@ -184,7 +184,7 @@ The module defines the following items:
		attribute instead.


		.. function:: compress(data, compresslevel=9, *, mtime=0)
		.. function:: compress(data, compresslevel=6, *, mtime=0)

		Compress the data, returning a :class:`bytes` object containing
		the compressed data. compresslevel and mtime have the same meaning as in
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1911,7 +1911,7 @@ def taropen(cls, name, mode="r", fileobj=None, **kwargs):
		return cls(name, mode, fileobj, **kwargs)

		@classmethod
		def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
		def gzopen(cls, name, mode="r", fileobj=None, compresslevel=6, **kwargs):
		"""Open gzip compressed tar archive name for reading or writing.
		Appending is not allowed.
		"""
Expand DownExpand Up		@@ -1944,7 +1944,7 @@ def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
		return t

		@classmethod
		def bz2open(cls, name, mode="r", fileobj=None, compresslevel=9, **kwargs):
		def bz2open(cls, name, mode="r", fileobj=None, compresslevel=6, **kwargs):
		"""Open bzip2 compressed tar archive name for reading or writing.
		Appending is not allowed.
		"""
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Adjust default compression level to 6 (down from 9) in gzip and tarfile.
		It is the default level used by most compression tools and a better
		tradeoff between speed and performance.