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GH-51229: [Python] Raise instead of crashing on unopened resize #51246

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1fanwang wants to merge 2 commits into apache:main

from 1fanwang:1fannnw/gh-51229-memory-mapped-file-resize

+6 −0

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GH-51229: [Python] Raise instead of crashing on unopened resize #51246

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GH-51229: [Python] Check MemoryMappedFile before resize

1fanwang Sep 8, 2026

GH-51229: Assert the value error with pytest.raises

1fanwang Sep 10, 2026

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1 change: 1 addition & 0 deletions python/pyarrow/io.pxi

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1101,6 +1101,7 @@ cdef class MemoryMappedFile(NativeFile):
		----------
		new_size : new size in bytes
		"""
	self._assert_open()
		check_status(self.handle.get().Resize(new_size))

		def fileno(self):
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5 changes: 5 additions & 0 deletions python/pyarrow/tests/test_io.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1216,6 +1216,11 @@ def test_memory_map_resize(tmpdir):
		assert f.read() == bytes(arr[:SIZE])


	def test_memory_map_resize_uninitialized():
Comment thread 1fanwang marked this conversation as resolved.
	with pytest.raises(ValueError, match="I/O operation on closed file"):
	pa.MemoryMappedFile().resize(0)


Comment on lines +1219 to +1223 @1fanwang 1fanwang Sep 10, 2026 Copy link Copy Markdown Contributor Author Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Keeping it in-process per #51246 (comment); with the fix it raises rather than crashing. @AlenkaF AlenkaF Sep 11, 2026 Copy link Copy Markdown Member Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Only the PR description needs an update.
		def test_memory_zero_length(tmpdir):
		path = os.path.join(str(tmpdir), guid())
		f = open(path, 'wb')
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