Add a test for a feature added in rev. 2.82 of typeobject.c:

- SLOT1BINFULL() macro: changed this to check for __rop__ overriding
  __op__, like binary_op1() in abstract.c -- the latter only calls the
  slot function once if both types use the same slot function, so the
  slot function must make both calls -- which it already did for the
  __op__, __rop__ order, but not yet for the __rop__, __op__ order
  when B.__class__ is a subclass of A.__class__.

Also test the refinement added in rev. 2.201 that fixes the problem
reported in SF bug #623669.

Also test a similar provision in abstract.c's binary_op1().

Lib/test/test_descr.py

@@ -3634,6 +3634,58 @@ def mutable_names():
     C.__name__ = 'D.E'
     vereq((C.__module__, C.__name__), (mod, 'D.E'))
 
+def subclass_right_op():
+    if verbose:
+        print "Testing correct dispatch of subclass overloading __r<op>__..."
+
+    # This code tests various cases where right-dispatch of a subclass
+    # should be preferred over left-dispatch of a base class.
+
+    # Case 1: subclass of int; this tests code in abstract.c::binary_op1()
+
+    class B(int):
+        def __div__(self, other):
+            return "B.__div__"
+        def __rdiv__(self, other):
+            return "B.__rdiv__"
+
+    vereq(B(1) / 1, "B.__div__")
+    vereq(1 / B(1), "B.__rdiv__")
+
+    # Case 2: subclass of object; this is just the baseline for case 3
+
+    class C(object):
+        def __div__(self, other):
+            return "C.__div__"
+        def __rdiv__(self, other):
+            return "C.__rdiv__"
+
+    vereq(C(1) / 1, "C.__div__")
+    vereq(1 / C(1), "C.__rdiv__")
+
+    # Case 3: subclass of new-style class; here it gets interesting
+
+    class D(C):
+        def __div__(self, other):
+            return "D.__div__"
+        def __rdiv__(self, other):
+            return "D.__rdiv__"
+
+    vereq(D(1) / C(1), "D.__div__")
+    vereq(C(1) / D(1), "D.__rdiv__")
+
+    # Case 4: this didn't work right in 2.2.2 and 2.3a1
+
+    class E(C):
+        pass
+
+    vereq(E.__rdiv__, C.__rdiv__)
+
+    vereq(E(1) / 1, "C.__div__")
+    vereq(1 / E(1), "C.__rdiv__")
+    vereq(E(1) / C(1), "C.__div__")
+    vereq(C(1) / E(1), "C.__div__") # This one would fail
+
 
 def test_main():
     do_this_first()
@@ -3718,6 +3770,7 @@ def test_main():
     test_mutable_bases_with_failing_mro()
     test_mutable_bases_catch_mro_conflict()
     mutable_names()
+    subclass_right_op()
 
     if verbose: print "All OK"