From 2aa86b80ebbbd2e0e7af316560ce18cbc39ec1b0 Mon Sep 17 00:00:00 2001
From: Hugo van Kemenade <hugovk@users.noreply.github.com>
Date: Wed, 2 Feb 2022 09:05:53 +0200
Subject: [PATCH] bpo-46607: Add DeprecationWarning for LegacyInterpolation,
 deprecated in docs since 3.2

---
 Doc/whatsnew/3.11.rst                                    | 5 +++++
 Lib/configparser.py                                      | 9 +++++++++
 Lib/test/test_configparser.py                            | 8 ++++++++
 .../Library/2022-01-26-18-30-34.bpo-46607.xnhT4a.rst     | 3 +++
 4 files changed, 25 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2022-01-26-18-30-34.bpo-46607.xnhT4a.rst

diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 18d4652fb42930..e89027e75767d8 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -473,6 +473,11 @@ Deprecated
 
   (Contributed by Hugo van Kemenade in :issue:`45173`.)
 
+* :class:`configparser.LegacyInterpolation` has been deprecated in the docstring
+  since Python 3.2. It now emits a :exc:`DeprecationWarning` and will be removed
+  in Python 3.13. Use :class:`configparser.BasicInterpolation` or
+  :class:`configparser.ExtendedInterpolation instead.
+  (Contributed by Hugo van Kemenade in :issue:`46607`.)
 
 Removed
 =======
diff --git a/Lib/configparser.py b/Lib/configparser.py
index 3470624e63f61b..cbf0f9c35268d3 100644
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -525,6 +525,15 @@ class LegacyInterpolation(Interpolation):
 
     _KEYCRE = re.compile(r"%\(([^)]*)\)s|.")
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        warnings.warn(
+            "LegacyInterpolation has been deprecated since Python 3.2 "
+            "and will be removed from the configparser module in Python 3.13. "
+            "Use BasicInterpolation or ExtendedInterpolation instead.",
+            DeprecationWarning, stacklevel=2
+        )
+
     def before_get(self, parser, section, option, value, vars):
         rawval = value
         depth = MAX_INTERPOLATION_DEPTH
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index e9b03e6c62ef14..f24e70ba1785fb 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -1658,6 +1658,14 @@ def test_safeconfigparser_deprecation(self):
         for warning in w:
             self.assertTrue(warning.category is DeprecationWarning)
 
+    def test_legacyinterpolation_deprecation(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always", DeprecationWarning)
+            configparser.LegacyInterpolation()
+        self.assertGreaterEqual(len(w), 1)
+        for warning in w:
+            self.assertIs(warning.category, DeprecationWarning)
+
     def test_sectionproxy_repr(self):
         parser = configparser.ConfigParser()
         parser.read_string("""
diff --git a/Misc/NEWS.d/next/Library/2022-01-26-18-30-34.bpo-46607.xnhT4a.rst b/Misc/NEWS.d/next/Library/2022-01-26-18-30-34.bpo-46607.xnhT4a.rst
new file mode 100644
index 00000000000000..e0c7ed0531b575
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-01-26-18-30-34.bpo-46607.xnhT4a.rst
@@ -0,0 +1,3 @@
+Add :exc:`DeprecationWarning` to :class:`LegacyInterpolation`, deprecated in
+the docstring since Python 3.2. Will be removed in Python 3.13. Use
+:class:`BasicInterpolation` or :class:`ExtendedInterpolation` instead.