[2.7] bpo-32137: The repr of deeply nested dict now raises a RuntimeError (GH-4570) (#5493)

instead of crashing due to a stack overflow.

This perhaps will fix similar problems in other extension types.
(cherry picked from commit 1fb72d2ad243c965d4432b4e93884064001a2607)
diff --git a/Lib/test/mapping_tests.py b/Lib/test/mapping_tests.py
index f43750b..248dee2 100644
--- a/Lib/test/mapping_tests.py
+++ b/Lib/test/mapping_tests.py
@@ -2,6 +2,7 @@
 import unittest
 import UserDict
 import test_support
+import sys
 
 
 class BasicTestMappingProtocol(unittest.TestCase):
@@ -645,6 +646,14 @@
         d = self._full_mapping({1: BadRepr()})
         self.assertRaises(Exc, repr, d)
 
+    def test_repr_deep(self):
+        d = self._empty_mapping()
+        for i in range(sys.getrecursionlimit() + 100):
+            d0 = d
+            d = self._empty_mapping()
+            d[1] = d0
+        self.assertRaises(RuntimeError, repr, d)
+
     def test_le(self):
         self.assertTrue(not (self._empty_mapping() < self._empty_mapping()))
         self.assertTrue(not (self._full_mapping({1: 2}) < self._full_mapping({1L: 2L})))