[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 1fb72d2a)

Lib/test/list_tests.py

@@ -45,10 +45,11 @@ class CommonTest(seq_tests.CommonTest):
         self.assertEqual(str(a2), "[0, 1, 2, [...], 3]")
         self.assertEqual(repr(a2), "[0, 1, 2, [...], 3]")
 
-        l0 = []
-        for i in xrange(sys.getrecursionlimit() + 100):
-            l0 = [l0]
-        self.assertRaises(RuntimeError, repr, l0)
+    def test_repr_deep(self):
+        a = self.type2test([])
+        for i in range(sys.getrecursionlimit() + 100):
+            a = self.type2test([a])
+        self.assertRaises(RuntimeError, repr, a)
 
     def test_print(self):
         d = self.type2test(xrange(200))

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 @@ class TestHashMappingProtocol(TestMappingProtocol):
         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})))

Lib/test/test_dict.py

@@ -3,6 +3,7 @@ from test import test_support
 
 import UserDict, random, string
 import gc, weakref
+import sys
 
 
 class DictTest(unittest.TestCase):
@@ -422,6 +423,12 @@ class DictTest(unittest.TestCase):
         d = {1: BadRepr()}
         self.assertRaises(Exc, repr, d)
 
+    def test_repr_deep(self):
+        d = {}
+        for i in range(sys.getrecursionlimit() + 100):
+            d = {1: d}
+        self.assertRaises(RuntimeError, repr, d)
+
     def test_le(self):
         self.assertFalse({} < {})
         self.assertFalse({1: 2} < {1L: 2L})

Misc/NEWS.d/next/Core and Builtins/2017-11-26-14-36-30.bpo-32137.Stj5nL.rst

+The repr of deeply nested dict now raises a RecursionError instead of
+crashing due to a stack overflow.

Objects/listobject.c

@@ -383,10 +383,7 @@ list_repr(PyListObject *v)
        so must refetch the list size on each iteration. */
     for (i = 0; i < Py_SIZE(v); ++i) {
         int status;
-        if (Py_EnterRecursiveCall(" while getting the repr of a list"))
-            goto Done;
         s = PyObject_Repr(v->ob_item[i]);
-        Py_LeaveRecursiveCall();
         if (s == NULL)
             goto Done;
         status = PyList_Append(pieces, s);

Objects/object.c

@@ -378,7 +378,12 @@ PyObject_Repr(PyObject *v)
                                    Py_TYPE(v)->tp_name, v);
     else {
         PyObject *res;
+        /* It is possible for a type to have a tp_repr representation that
+           loops infinitely. */
+        if (Py_EnterRecursiveCall(" while getting the repr of an object"))
+            return NULL;
         res = (*Py_TYPE(v)->tp_repr)(v);
+        Py_LeaveRecursiveCall();
         if (res == NULL)
             return NULL;
 #ifdef Py_USING_UNICODE

Objects/tupleobject.c

@@ -288,10 +288,7 @@ tuplerepr(PyTupleObject *v)
 
     /* Do repr() on each element. */
     for (i = 0; i < n; ++i) {
-        if (Py_EnterRecursiveCall(" while getting the repr of a tuple"))
-            goto Done;
         s = PyObject_Repr(v->ob_item[i]);
-        Py_LeaveRecursiveCall();
         if (s == NULL)
             goto Done;
         PyTuple_SET_ITEM(pieces, i, s);