gh-125260: gzip: let compress mtime default to 0

Doc/library/gzip.rst

@@ -184,11 +184,12 @@ The module defines the following items:
  attribute instead.
 
 
-.. function:: compress(data, compresslevel=9, *, mtime=None)
+.. function:: compress(data, compresslevel=9, *, mtime=0)
 
  Compress the *data*, returning a :class:`bytes` object containing
  the compressed data. *compresslevel* and *mtime* have the same meaning as in
- the :class:`GzipFile` constructor above.
+ the :class:`GzipFile` constructor above,
+ but *mtime* defaults to 0 for reproducible output.
 
  .. versionadded:: 3.2
  .. versionchanged:: 3.8
@@ -203,6 +204,10 @@ The module defines the following items:
  .. versionchanged:: 3.13
  The gzip header OS byte is guaranteed to be set to 255 when this function
  is used as was the case in 3.10 and earlier.
+ .. versionchanged:: 3.14
+ The *mtime* parameter now defaults to 0 for reproducible output.
+ For the previous behaviour of using the current time,
+ pass ``None`` to *mtime*.
 
 .. function:: decompress(data)
 

Lib/gzip.py

@@ -580,12 +580,12 @@ def _rewind(self):
  self._new_member = True
 
 
-def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=None):
+def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=0):
  """Compress data in one shot and return the compressed string.
 
  compresslevel sets the compression level in range of 0-9.
- mtime can be used to set the modification time. The modification time is
- set to the current time by default.
+ mtime can be used to set the modification time.
+ The modification time is set to 0 by default, for reproducibility.
  """
  # Wbits=31 automatically includes a gzip header and trailer.
  gzip_data = zlib.compress(data, level=compresslevel, wbits=31)

Lib/test/test_gzip.py

@@ -713,6 +713,17 @@ def test_compress_mtime(self):
  f.read(1) # to set mtime attribute
  self.assertEqual(f.mtime, mtime)
 
+ def test_compress_mtime_default(self):
+ # test for gh-125260
+ datac = gzip.compress(data1, mtime=0)
+ datac2 = gzip.compress(data1)
+ self.assertEqual(datac, datac2)
+ datac3 = gzip.compress(data1, mtime=None)
+ self.assertNotEqual(datac, datac3)
+ with gzip.GzipFile(fileobj=io.BytesIO(datac3), mode="rb") as f:
+ f.read(1) # to set mtime attribute
+ self.assertGreater(f.mtime, 1)
+
  def test_compress_correct_level(self):
  for mtime in (0, 42):
  with self.subTest(mtime=mtime):

Misc/NEWS.d/next/Library/2024-10-11-04-04-38.gh-issue-125260.PeZ0Mb.rst

@@ -0,0 +1,2 @@
+The :func:`gzip.compress` *mtime* parameter now defaults to 0 for reproducible output.
+Patch by Bernhard M. Wiedemann and Adam Turner.