From bdc34d273f3ef71cd0aad9808b1d0cca7505d195 Mon Sep 17 00:00:00 2001
From: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Date: Fri, 6 Mar 2026 15:03:29 +0200
Subject: [PATCH] Support frozendict in plistlib

---
 Doc/library/plistlib.rst  |  6 +++---
 Lib/plistlib.py           | 20 ++++++++++----------
 Lib/test/test_plistlib.py | 19 +++++++++++++++++++
 3 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/Doc/library/plistlib.rst b/Doc/library/plistlib.rst
index e5fc19f495226e..dd1ba11da5d301 100644
--- a/Doc/library/plistlib.rst
+++ b/Doc/library/plistlib.rst
@@ -18,7 +18,7 @@ and XML plist files.
 
 The property list (``.plist``) file format is a simple serialization supporting
 basic object types, like dictionaries, lists, numbers and strings.  Usually the
-top level object is a dictionary.
+top level object is a dictionary or frozen dictionary.
 
 To write out and to parse a plist file, use the :func:`dump` and
 :func:`load` functions.
@@ -183,12 +183,12 @@ Generating a plist::
     import datetime
     import plistlib
 
-    pl = dict(
+    pl = frozendict(
         aString = "Doodah",
         aList = ["A", "B", 12, 32.1, [1, 2, 3]],
         aFloat = 0.1,
         anInt = 728,
-        aDict = dict(
+        aDict = frozendict(
             anotherString = "<hello & hi there!>",
             aThirdString = "M\xe4ssig, Ma\xdf",
             aTrueValue = True,
diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index 3c6a6b7bdc44d2..88b1e8e0507587 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -2,7 +2,7 @@
 
 The property list (.plist) file format is a simple XML pickle supporting
 basic object types, like dictionaries, lists, numbers and strings.
-Usually the top level object is a dictionary.
+Usually the top level object is a dictionary or frozen dictionary.
 
 To write out a plist file, use the dump(value, file)
 function. 'value' is the top level object, 'file' is
@@ -24,12 +24,12 @@
     import datetime
     import plistlib
 
-    pl = dict(
+    pl = frozendict(
         aString = "Doodah",
         aList = ["A", "B", 12, 32.1, [1, 2, 3]],
         aFloat = 0.1,
         anInt = 728,
-        aDict = dict(
+        aDict = frozendict(
             anotherString = "<hello & hi there!>",
             aThirdString = "M\xe4ssig, Ma\xdf",
             aTrueValue = True,
@@ -357,7 +357,7 @@ def write_value(self, value):
         elif isinstance(value, float):
             self.simple_element("real", repr(value))
 
-        elif isinstance(value, dict):
+        elif isinstance(value, (dict, frozendict)):
             self.write_dict(value)
 
         elif isinstance(value, (bytes, bytearray)):
@@ -715,7 +715,7 @@ def _flatten(self, value):
             self._objidtable[id(value)] = refnum
 
         # And finally recurse into containers
-        if isinstance(value, dict):
+        if isinstance(value, (dict, frozendict)):
             keys = []
             values = []
             items = value.items()
@@ -836,7 +836,7 @@ def _write_object(self, value):
             self._write_size(0xA0, s)
             self._fp.write(struct.pack('>' + self._ref_format * s, *refs))
 
-        elif isinstance(value, dict):
+        elif isinstance(value, (dict, frozendict)):
             keyRefs, valRefs = [], []
 
             if self._sort_keys:
@@ -869,18 +869,18 @@ def _is_fmt_binary(header):
 # Generic bits
 #
 
-_FORMATS={
-    FMT_XML: dict(
+_FORMATS=frozendict({
+    FMT_XML: frozendict(
         detect=_is_fmt_xml,
         parser=_PlistParser,
         writer=_PlistWriter,
     ),
-    FMT_BINARY: dict(
+    FMT_BINARY: frozendict(
         detect=_is_fmt_binary,
         parser=_BinaryPlistParser,
         writer=_BinaryPlistWriter,
     )
-}
+})
 
 
 def load(fp, *, fmt=None, dict_type=dict, aware_datetime=False):
diff --git a/Lib/test/test_plistlib.py b/Lib/test/test_plistlib.py
index d9216be4d95658..b9c261310bb567 100644
--- a/Lib/test/test_plistlib.py
+++ b/Lib/test/test_plistlib.py
@@ -792,6 +792,25 @@ def test_dict_members(self):
                 })
                 self.assertIsNot(pl2['first'], pl2['second'])
 
+    def test_frozendict(self):
+        pl = frozendict(
+            aString="Doodah",
+            anInt=728,
+            aDict=frozendict(
+                anotherString="hello",
+                aTrueValue=True,
+            ),
+            aList=["A", "B", 12],
+        )
+
+        for fmt in ALL_FORMATS:
+            with self.subTest(fmt=fmt):
+                data = plistlib.dumps(pl, fmt=fmt)
+                pl2 = plistlib.loads(data)
+                self.assertEqual(pl2, dict(pl))
+                self.assertIsInstance(pl2, dict)
+                self.assertIsInstance(pl2['aDict'], dict)
+
     def test_controlcharacters(self):
         for i in range(128):
             c = chr(i)