diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index c9d96085ef739d..c59014a6f5bdce 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -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`.
@@ -59,6 +59,11 @@ The module defines the following items:
.. versionchanged:: 3.6
Accepts a :term:`path-like object`.
+ .. versionchanged:: next
+ The default compression level was reduced to 6 (down from 9).
+ It is the default level used by most compression tools and a better
+ tradeoff between speed and performance.
+
.. exception:: BadGzipFile
An exception raised for invalid gzip files. It inherits from :exc:`OSError`.
@@ -67,7 +72,7 @@ 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`
@@ -181,8 +186,13 @@ The module defines the following items:
Remove the ``filename`` attribute, use the :attr:`~GzipFile.name`
attribute instead.
+ .. versionchanged:: next
+ The default compression level was reduced to 6 (down from 9).
+ It is the default level used by most compression tools and a better
+ tradeoff between speed and performance.
+
-.. 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
@@ -206,6 +216,10 @@ The module defines the following items:
The *mtime* parameter now defaults to 0 for reproducible output.
For the previous behaviour of using the current time,
pass ``None`` to *mtime*.
+ .. versionchanged:: next
+ The default compression level was reduced to 6 (down from 9).
+ It is the default level used by most compression tools and a better
+ tradeoff between speed and performance.
.. function:: decompress(data)
diff --git a/Doc/library/tarfile.rst b/Doc/library/tarfile.rst
index 7cec108a5bd41d..d496c0d7793756 100644
--- a/Doc/library/tarfile.rst
+++ b/Doc/library/tarfile.rst
@@ -110,7 +110,7 @@ Some facts and figures:
For modes ``'w:gz'``, ``'x:gz'``, ``'w|gz'``, ``'w:bz2'``, ``'x:bz2'``,
``'w|bz2'``, :func:`tarfile.open` accepts the keyword argument
- *compresslevel* (default ``9``) to specify the compression level of the file.
+ *compresslevel* (default ``6``) to specify the compression level of the file.
For modes ``'w:xz'``, ``'x:xz'`` and ``'w|xz'``, :func:`tarfile.open` accepts the
keyword argument *preset* to specify the compression level of the file.
@@ -170,6 +170,10 @@ Some facts and figures:
.. versionchanged:: 3.14
The *preset* keyword argument also works for streams.
+ .. versionchanged:: next
+ The default compression level was reduced to 6 (down from 9).
+ It is the default level used by most compression tools and a better
+ tradeoff between speed and performance.
.. class:: TarFile
:noindex:
diff --git a/Lib/gzip.py b/Lib/gzip.py
index c00f51858de0f0..89c4738ec69325 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -30,7 +30,7 @@
_WRITE_BUFFER_SIZE = 4 * io.DEFAULT_BUFFER_SIZE
-def open(filename, mode="rb", compresslevel=_COMPRESS_LEVEL_BEST,
+def open(filename, mode="rb", compresslevel=_COMPRESS_LEVEL_TRADEOFF,
encoding=None, errors=None, newline=None):
"""Open a gzip-compressed file in binary or text mode.
@@ -158,7 +158,7 @@ class GzipFile(_streams.BaseStream):
myfileobj = None
def __init__(self, filename=None, mode=None,
- compresslevel=_COMPRESS_LEVEL_BEST, fileobj=None, mtime=None):
+ compresslevel=_COMPRESS_LEVEL_TRADEOFF, fileobj=None, mtime=None):
"""Constructor for the GzipFile class.
At least one of fileobj and filename must be given a
@@ -621,7 +621,7 @@ def _rewind(self):
self._new_member = True
-def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=0):
+def compress(data, compresslevel=_COMPRESS_LEVEL_TRADEOFF, *, mtime=0):
"""Compress data in one shot and return the compressed string.
compresslevel sets the compression level in range of 0-9.
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 068aa13ed70356..80d8644af86f74 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1927,7 +1927,7 @@ def not_compressed(comptype):
if "preset" in kwargs and comptype not in ("xz",):
raise ValueError("preset is only valid for w|xz mode")
- compresslevel = kwargs.pop("compresslevel", 9)
+ compresslevel = kwargs.pop("compresslevel", 6)
preset = kwargs.pop("preset", None)
stream = _Stream(name, filemode, comptype, fileobj, bufsize,
compresslevel, preset)
@@ -1953,7 +1953,7 @@ 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.
"""
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
index a12ff5662a73db..9a2e1dd248fe94 100644
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -353,7 +353,7 @@ def test_mtime(self):
def test_metadata(self):
mtime = 123456789
- with gzip.GzipFile(self.filename, 'w', mtime = mtime) as fWrite:
+ with gzip.GzipFile(self.filename, 'w', mtime = mtime, compresslevel = 9) as fWrite:
fWrite.write(data1)
with open(self.filename, 'rb') as fRead:
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
new file mode 100644
index 00000000000000..0e866fa4ef6169
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-03-19-12-41-42.gh-issue-91349.8eTOCP.rst
@@ -0,0 +1,3 @@
+Adjust default ``compressionlevel=`` to 6 (down from 9) in :mod:`gzip` and :mod:`tarfile`.
+It is the default level used by most compression tools and a better
+tradeoff between speed and performance.
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