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gh-70999: Preserve caller vars in ExtendedInterpolation nested interpolation #155880

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gh-70999: Preserve caller vars in ExtendedInterpolation nested interpolation #155880

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7 changes: 5 additions & 2 deletions Lib/configparser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -547,9 +547,12 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
if v is None:
continue
if "$" in v:
if sect == section:
submap = map
else:
submap = dict(parser.items(sect, raw=True))
self._interpolate_some(parser, opt, accum, v, sect,
dict(parser.items(sect, raw=True)),
depth + 1)
submap, depth + 1)
else:
accum.append(v)
else:
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24 changes: 24 additions & 0 deletions Lib/test/test_configparser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1334,6 +1334,30 @@ def test_other_errors(self):
with self.assertRaises(ValueError):
cf['interpolation fail']['case6'] = "BLACK $ABBATH"

def test_get_with_vars_nested(self):
# gh-70999: caller-supplied ``vars`` must be honoured at every level
# of a same-section interpolation chain, not just the first.
cf = self.fromstring(textwrap.dedent("""
[section]
a = ${b}
b = ${c}
c = default

[cross]
via = ${section:c}
""").strip())

eq = self.assertEqual
# Directly referencing the overridden option already worked.
eq(cf.get('section', 'b', vars={'c': 'OVERRIDE'}), 'OVERRIDE')
# Reaching it through another same-section option must too.
eq(cf.get('section', 'a', vars={'c': 'OVERRIDE'}), 'OVERRIDE')
# Without an override the configured value is still used.
eq(cf.get('section', 'a'), 'default')
# ``vars`` are scoped to the requested section and must not leak
# into a different section reached via ``${section:option}``.
eq(cf.get('cross', 'via', vars={'c': 'OVERRIDE'}), 'default')


class ConfigParserTestCaseNoValue(ConfigParserTestCase):
allow_no_value = True
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-08-15-12-00-00.gh-issue-70999.NZ96LZ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :class:`configparser.ExtendedInterpolation` dropping caller-supplied
``vars`` during nested interpolation within a section. Patch by Nikolaus
Schuetz.
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