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[3.14] gh-136170: Revert adding ZipFile.data_offset (GH-136950) #136955

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Merged
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Jul 22, 2025
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[3.14] gh-136170: Revert adding ZipFile.data_offset (GH-136950) #136955

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8 changes: 0 additions & 8 deletions Doc/library/zipfile.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -558,14 +558,6 @@ The following data attributes are also available:
it should be no longer than 65535 bytes. Comments longer than this will be
truncated.

.. attribute:: ZipFile.data_offset

The offset to the start of ZIP data from the beginning of the file. When the
:class:`ZipFile` is opened in either mode ``'w'`` or ``'x'`` and the
underlying file does not support ``tell()``, the value will be ``None``
instead.

.. versionadded:: 3.14

.. _path-objects:

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54 changes: 0 additions & 54 deletions Lib/test/test_zipfile/test_core.py
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Expand Up @@ -3470,60 +3470,6 @@ def test_execute_zip64(self):
self.assertIn(b'number in executable: 5', output)


class TestDataOffsetPrependedZip(unittest.TestCase):
"""Test .data_offset on reading zip files with an executable prepended."""

def setUp(self):
self.exe_zip = findfile('exe_with_zip', subdir='archivetestdata')
self.exe_zip64 = findfile('exe_with_z64', subdir='archivetestdata')

def _test_data_offset(self, name):
with zipfile.ZipFile(name) as zipfp:
self.assertEqual(zipfp.data_offset, 713)

def test_data_offset_with_exe_prepended(self):
self._test_data_offset(self.exe_zip)

def test_data_offset_with_exe_prepended_zip64(self):
self._test_data_offset(self.exe_zip64)

class TestDataOffsetZipWrite(unittest.TestCase):
"""Test .data_offset for ZipFile opened in write mode."""

def setUp(self):
os.mkdir(TESTFNDIR)
self.addCleanup(rmtree, TESTFNDIR)
self.test_path = os.path.join(TESTFNDIR, 'testoffset.zip')

def test_data_offset_write_no_prefix(self):
with io.BytesIO() as fp:
with zipfile.ZipFile(fp, "w") as zipfp:
self.assertEqual(zipfp.data_offset, 0)

def test_data_offset_write_with_prefix(self):
with io.BytesIO() as fp:
fp.write(b"this is a prefix")
with zipfile.ZipFile(fp, "w") as zipfp:
self.assertEqual(zipfp.data_offset, 16)

def test_data_offset_append_with_bad_zip(self):
with io.BytesIO() as fp:
fp.write(b"this is a prefix")
with zipfile.ZipFile(fp, "a") as zipfp:
self.assertEqual(zipfp.data_offset, 16)

def test_data_offset_write_no_tell(self):
# The initializer in ZipFile checks if tell raises AttributeError or
# OSError when creating a file in write mode when deducing the offset
# of the beginning of zip data
class NoTellBytesIO(io.BytesIO):
def tell(self):
raise OSError("Unimplemented!")
with NoTellBytesIO() as fp:
with zipfile.ZipFile(fp, "w") as zipfp:
self.assertIsNone(zipfp.data_offset)


class EncodedMetadataTests(unittest.TestCase):
file_names = ['\u4e00', '\u4e8c', '\u4e09'] # Han 'one', 'two', 'three'
file_content = [
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13 changes: 0 additions & 13 deletions Lib/zipfile/__init__.py
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Expand Up @@ -1452,7 +1452,6 @@ def __init__(self, file, mode="r", compression=ZIP_STORED, allowZip64=True,
self._lock = threading.RLock()
self._seekable = True
self._writing = False
self._data_offset = None

try:
if mode == 'r':
Expand All @@ -1463,7 +1462,6 @@ def __init__(self, file, mode="r", compression=ZIP_STORED, allowZip64=True,
self._didModify = True
try:
self.start_dir = self.fp.tell()
self._data_offset = self.start_dir
except (AttributeError, OSError):
self.fp = _Tellable(self.fp)
self.start_dir = 0
Expand All @@ -1488,7 +1486,6 @@ def __init__(self, file, mode="r", compression=ZIP_STORED, allowZip64=True,
# even if no files are added to the archive
self._didModify = True
self.start_dir = self.fp.tell()
self._data_offset = self.start_dir
else:
raise ValueError("Mode must be 'r', 'w', 'x', or 'a'")
except:
Expand Down Expand Up @@ -1535,10 +1532,6 @@ def _RealGetContents(self):
# self.start_dir: Position of start of central directory
self.start_dir = offset_cd + concat

# store the offset to the beginning of data for the
# .data_offset property
self._data_offset = concat

if self.start_dir < 0:
raise BadZipFile("Bad offset for central directory")
fp.seek(self.start_dir, 0)
Expand Down Expand Up @@ -1599,12 +1592,6 @@ def _RealGetContents(self):
zinfo._end_offset = end_offset
end_offset = zinfo.header_offset

@property
def data_offset(self):
"""The offset to the start of zip data in the file or None if
unavailable."""
return self._data_offset

def namelist(self):
"""Return a list of file names in the archive."""
return [data.filename for data in self.filelist]
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2025-07-21-22-35-50.gh-issue-136170.QUlc78.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Removed the unreleased ``zipfile.ZipFile.data_offset`` property added in 3.14.0a7
as it wasn't fully clear which behavior it should have in some situations so
the result was not always what a user might expect.
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