diff -r 135a0d7bc4db Lib/test/test_class.py
--- a/Lib/test/test_class.py	Sun Mar 20 10:44:30 2011 +0800
+++ b/Lib/test/test_class.py	Sun Mar 20 05:44:49 2011 +0100
@@ -545,6 +545,16 @@
         a = A(hash(A.f)^(-1))
         hash(a.f)
 
+    def testNoCrashIfStrIsRepr(self):
+        # See issue #11603
+        class Foo:
+            pass
+        Foo.__repr__ = Foo.__str__
+
+        foo = Foo()
+        # The following line resulted in a crash or infinite loop
+        str(foo)
+
 def test_main():
     support.run_unittest(ClassTests)
 
diff -r 135a0d7bc4db Objects/typeobject.c
--- a/Objects/typeobject.c	Sun Mar 20 10:44:30 2011 +0800
+++ b/Objects/typeobject.c	Sun Mar 20 05:44:49 2011 +0100
@@ -2821,7 +2821,7 @@
     unaryfunc f;
 
     f = Py_TYPE(self)->tp_repr;
-    if (f == NULL)
+    if (f == NULL || f == object_str)
         f = object_repr;
     return f(self);
 }