From 3ee6dabf5b2bcfe5aa27a6db4f7adb7d7f33f8d6 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Tue, 21 May 2013 12:47:57 +0300
Subject: [PATCH] Issue #17900: Allowed pickling of recursive OrderedDicts. 
 Decreased pickled size and pickling time.

---
 Lib/collections/__init__.py  |  5 +----
 Lib/test/test_collections.py | 13 +++++++++++--
 Misc/NEWS                    |  3 +++
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 5fd54e8d4cb..e1a075c7585 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -199,13 +199,10 @@ class OrderedDict(dict):
 
     def __reduce__(self):
         'Return state information for pickling'
-        items = [[k, self[k]] for k in self]
         inst_dict = vars(self).copy()
         for k in vars(OrderedDict()):
             inst_dict.pop(k, None)
-        if inst_dict:
-            return (self.__class__, (items,), inst_dict)
-        return self.__class__, (items,)
+        return self.__class__, (), inst_dict or None, None, iter(self.items())
 
     def copy(self):
         'od.copy() -> a shallow copy of od'
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 80330312594..8f379eff552 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -1245,9 +1245,18 @@ class TestOrderedDict(unittest.TestCase):
         # do not save instance dictionary if not needed
         pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
         od = OrderedDict(pairs)
-        self.assertEqual(len(od.__reduce__()), 2)
+        self.assertIsNone(od.__reduce__()[2])
         od.x = 10
-        self.assertEqual(len(od.__reduce__()), 3)
+        self.assertIsNotNone(od.__reduce__()[2])
+
+    def test_pickle_recursive(self):
+        od = OrderedDict()
+        od[1] = od
+        for proto in range(-1, pickle.HIGHEST_PROTOCOL + 1):
+            dup = pickle.loads(pickle.dumps(od, proto))
+            self.assertIsNot(dup, od)
+            self.assertEqual(list(dup.keys()), [1])
+            self.assertIs(dup[1], dup)
 
     def test_repr(self):
         od = OrderedDict([('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)])
diff --git a/Misc/NEWS b/Misc/NEWS
index acd89e40205..2027e65f3e8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -99,6 +99,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17900: Allowed pickling of recursive OrderedDicts.  Decreased pickled
+  size and pickling time.
+
 - Issue #17914: Add os.cpu_count(). Patch by Yogesh Chaudhari, based on an
   initial patch by Trent Nelson.