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gh-89756: make SpooledTemporaryFile.truncate return new file size and improve documentation #29197

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gh-89756: make SpooledTemporaryFile.truncate return new file size and improve documentation #29197

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717a927
pbo-45593: make SpooledTemporaryFile.truncate return new file size
rooterkyberian Oct 23, 2021
5ebc370
Merge branch 'main' into pbo-45593
rooterkyberian Jul 31, 2023
fa3b08f
fix versionchanged in Doc/library/tempfile.rst
rooterkyberian Aug 9, 2023
a1455f6
Merge branch 'main' into pbo-45593
methane May 11, 2026
1c40e9f
fix SpooledTemporaryFile docs
rooterkyberian May 11, 2026
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4 changes: 4 additions & 0 deletions Doc/library/tempfile.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -172,6 +172,9 @@ The module defines the following user-callable items:
:class:`io.TextIOBase` abstract base classes (depending on whether binary
or text *mode* was specified).

.. versionchanged:: 3.12
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The truncate method returns new file size.


.. class:: TemporaryDirectory(suffix=None, prefix=None, dir=None, ignore_cleanup_errors=False, *, delete=True)

Expand Down Expand Up @@ -388,6 +391,7 @@ Here are some examples of typical usage of the :mod:`tempfile` module::
>>> fp.write(b'Hello world!')
# read data from file
>>> fp.seek(0)
0

@methane methane Aug 10, 2023

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If we add 0 here, we should add 12 after fp.write(b'Hello world!') too.

@methane methane Aug 10, 2023

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And later,

    >>> with tempfile.TemporaryFile() as fp:
    ...     fp.write(b'Hello world!')
    ...     fp.seek(0)
    ...     fp.read()
    b'Hello world!'

This output should be:

12
0
b'Hello world!'

@methane methane Aug 10, 2023

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It seems this file is not tested by doctest.

Please leave it. Otherwise, we need to fix all output and remove all comments in sample code.

>>> fp.read()
b'Hello world!'
# close the file, it will be removed
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13 changes: 13 additions & 0 deletions Lib/test/test_tempfile.py
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Expand Up @@ -1470,6 +1470,19 @@ def test_truncate_with_size_parameter(self):
self.assertTrue(f._rolled)
self.assertEqual(os.fstat(f.fileno()).st_size, 20)

def test_truncate_return_size(self):
"SpooledTemporaryFile truncate should return new position"
f = tempfile.SpooledTemporaryFile(max_size=10)
f.write(b'abcdef')
self.assertEqual(f.truncate(3), 3)

def test_seek_return_position(self):
"SpooledTemporaryFile seek should return file position"
f = tempfile.SpooledTemporaryFile(max_size=10)
f.write(b'abcdef')
self.assertEqual(f.seek(3), 3)
self.assertEqual(f.seek(0, 2), 6)

def test_class_getitem(self):
self.assertIsInstance(tempfile.SpooledTemporaryFile[bytes],
types.GenericAlias)
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2021-10-24-01-28-07.bpo-45593.QjC6-D.rst
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@@ -0,0 +1 @@
Make :meth:`tempfile.SpooledTemporaryFile.truncate()` to return new file size.