[Python-checkins] gh-130941: Fix `configparser` parsing values with `allow_no_value` and `interpolation` set (GH-130949)

[ambv]

https://github.com/python/cpython/commit/c35c7353eb8fbccff2d3a6ab664426b31af00d4d
commit: c35c7353eb8fbccff2d3a6ab664426b31af00d4d
branch: main
author: sobolevn <m...@sobolevn.me>
committer: ambv <luk...@langa.pl>
date: 2025-04-16T12:39:11+02:00
summary:

gh-130941: Fix `configparser` parsing values with `allow_no_value` and 
`interpolation` set (GH-130949)

files:
A Misc/NEWS.d/next/Library/2025-03-07-17-47-32.gh-issue-130941.7_GvhW.rst
M Lib/configparser.py
M Lib/test/test_configparser.py

diff --git a/Lib/configparser.py b/Lib/configparser.py
index 70cc651edabd86..239fda60a02ca0 100644
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -541,6 +541,8 @@ def _interpolate_some(self, parser, option, accum, rest, 
section, map,
                 except (KeyError, NoSectionError, NoOptionError):
                     raise InterpolationMissingOptionError(
                         option, section, rawval, ":".join(path)) from None
+                if v is None:
+                    continue
                 if "$" in v:
                     self._interpolate_some(parser, opt, accum, v, sect,
                                            dict(parser.items(sect, raw=True)),
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index 1313ec2b9e884e..23904d17d326d8 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -1328,6 +1328,47 @@ class ConfigParserTestCaseNoValue(ConfigParserTestCase):
     allow_no_value = True
 
 
+class NoValueAndExtendedInterpolation(CfgParserTestCaseClass):
+    interpolation = configparser.ExtendedInterpolation()
+    allow_no_value = True
+
+    def test_interpolation_with_allow_no_value(self):
+        config = textwrap.dedent("""
+            [dummy]
+            a
+            b = ${a}
+        """)
+        cf = self.fromstring(config)
+
+        self.assertIs(cf["dummy"]["a"], None)
+        self.assertEqual(cf["dummy"]["b"], "")
+
+    def test_explicit_none(self):
+        config = textwrap.dedent("""
+            [dummy]
+            a = None
+            b = ${a}
+        """)
+        cf = self.fromstring(config)
+
+        self.assertEqual(cf["dummy"]["a"], "None")
+        self.assertEqual(cf["dummy"]["b"], "None")
+
+
+class ConfigParserNoValueAndExtendedInterpolationTest(
+    NoValueAndExtendedInterpolation,
+    unittest.TestCase,
+):
+    config_class = configparser.ConfigParser
+
+
+class RawConfigParserNoValueAndExtendedInterpolationTest(
+    NoValueAndExtendedInterpolation,
+    unittest.TestCase,
+):
+    config_class = configparser.RawConfigParser
+
+
 class ConfigParserTestCaseTrickyFile(CfgParserTestCaseClass, 
unittest.TestCase):
     config_class = configparser.ConfigParser
     delimiters = {'='}
diff --git 
a/Misc/NEWS.d/next/Library/2025-03-07-17-47-32.gh-issue-130941.7_GvhW.rst 
b/Misc/NEWS.d/next/Library/2025-03-07-17-47-32.gh-issue-130941.7_GvhW.rst
new file mode 100644
index 00000000000000..4f0cda8d03e902
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-03-07-17-47-32.gh-issue-130941.7_GvhW.rst
@@ -0,0 +1,2 @@
+Fix :class:`configparser.ConfigParser` parsing empty interpolation with
+``allow_no_value`` set to ``True``.

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