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gh-154596: Fix configparser write() losing unnamed-section items to DEFAULT #154597

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gh-154596: Fix configparser write() losing unnamed-section items to DEFAULT #154597

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4 changes: 2 additions & 2 deletions Lib/configparser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -971,11 +971,11 @@ def write(self, fp, space_around_delimiters=True):
d = " {} ".format(self._delimiters[0])
else:
d = self._delimiters[0]
if UNNAMED_SECTION in self._sections and self._sections[UNNAMED_SECTION]:
self._write_section(fp, UNNAMED_SECTION, self._sections[UNNAMED_SECTION].items(), d, unnamed=True)
if self._defaults:
self._write_section(fp, self.default_section,
self._defaults.items(), d)
if UNNAMED_SECTION in self._sections and self._sections[UNNAMED_SECTION]:
self._write_section(fp, UNNAMED_SECTION, self._sections[UNNAMED_SECTION].items(), d, unnamed=True)

for section in self._sections:
if section is UNNAMED_SECTION:
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11 changes: 11 additions & 0 deletions Lib/test/test_configparser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2250,6 +2250,17 @@ def test_add_section(self):
cfg.write(output)
self.assertEqual(output.getvalue(), 'a = 1\n\n')

def test_write_roundtrip_with_default(self):
US = configparser.UNNAMED_SECTION
cfg = configparser.ConfigParser(allow_unnamed_section=True)
cfg.read_string('key1 = val1\n[DEFAULT]\ndkey = dval\n[sect1]\nkey2 = val2\n')
out = io.StringIO()
cfg.write(out)
cfg2 = configparser.ConfigParser(allow_unnamed_section=True)
cfg2.read_string(out.getvalue())
self.assertIn('key1', cfg2[US])
self.assertNotIn('key1', cfg2.defaults())

def test_disabled_error(self):
with self.assertRaises(configparser.MissingSectionHeaderError):
configparser.ConfigParser().read_string("a = 1")
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-24-20-00-00.gh-issue-154596.CfgWrt.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :meth:`configparser.ConfigParser.write` outputting unnamed-section
items after the ``[DEFAULT]`` header, causing them to be absorbed into
DEFAULT on re-read. Patch by tonghuaroot.
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