From 69976a7fbe7b3296d97a1e3169ec2b361feadfa9 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Sun, 12 Sep 2010 05:28:42 +0000
Subject: [PATCH] Issue #9826:  Handle recursive repr in
 collections.OrderedDict.

---
 Lib/collections.py           | 16 ++++++++++++----
 Lib/test/test_collections.py |  7 +++++++
 Misc/NEWS                    |  3 +++
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/Lib/collections.py b/Lib/collections.py
index f255919f0f..4ac50d8a66 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -43,6 +43,7 @@ class OrderedDict(dict, MutableMapping):
         '''
         if len(args) > 1:
             raise TypeError('expected at most 1 arguments, got %d' % len(args))
+        self.__in_repr = False              # detects recursive repr
         try:
             self.__root
         except AttributeError:
@@ -100,10 +101,10 @@ class OrderedDict(dict, MutableMapping):
     def __reduce__(self):
         'Return state information for pickling'
         items = [[k, self[k]] for k in self]
-        tmp = self.__map, self.__root
-        del self.__map, self.__root
+        tmp = self.__map, self.__root, self.__in_repr
+        del self.__map, self.__root, self.__in_repr
         inst_dict = vars(self).copy()
-        self.__map, self.__root = tmp
+        self.__map, self.__root, self.__in_repr = tmp
         if inst_dict:
             return (self.__class__, (items,), inst_dict)
         return self.__class__, (items,)
@@ -128,9 +129,16 @@ class OrderedDict(dict, MutableMapping):
 
     def __repr__(self):
         'od.__repr__() <==> repr(od)'
+        if self.__in_repr:
+            return '...'
         if not self:
             return '%s()' % (self.__class__.__name__,)
-        return '%s(%r)' % (self.__class__.__name__, list(self.items()))
+        self.__in_repr = True
+        try:
+            result = '%s(%r)' % (self.__class__.__name__, list(self.items()))
+        finally:
+            self.__in_repr = False
+        return result
 
     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 5e22afc2a9..d4353303db 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -908,6 +908,13 @@ class TestOrderedDict(unittest.TestCase):
         self.assertEqual(eval(repr(od)), od)
         self.assertEqual(repr(OrderedDict()), "OrderedDict()")
 
+    def test_repr_recursive(self):
+        # See issue #9826
+        od = OrderedDict.fromkeys('abc')
+        od['x'] = od
+        self.assertEqual(repr(od),
+            "OrderedDict([('a', None), ('b', None), ('c', None), ('x', ...)])")
+
     def test_setdefault(self):
         pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
         shuffle(pairs)
diff --git a/Misc/NEWS b/Misc/NEWS
index 327186173e..0599cbcdc5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -122,6 +122,9 @@ Library
   to fetch the original errno, or to filter timeout errors.  Now the
   original error is re-raised.
 
+- Issue #9826: OrderedDict.__repr__ can now handle self-referential
+  values:   d['x'] = d.
+
 - Issue #9758: When fcntl.ioctl() was called with mutable_flag set to True,
   and the passed buffer was exactly 1024 bytes long, the buffer wouldn't
   be updated back after the system call.  Original patch by Brian Brazil.
-- 
2.40.0