For some reason (probably cut and paste), __ipow__ for new-style

classes was called with three arguments.  This makes no sense, there's
no way to pass in the "modulo" 3rd argument as for __pow__, and
classic classes don't do this.  [SF bug 620179]

I don't want to backport this to 2.2.2, because it could break
existing code that has developed a work-around.  Code in 2.2.2 that
wants to use __ipow__ and wants to be forward compatible with 2.3
should be written like this:

  def __ipow__(self, exponent, modulo=None):
      ...

Lib/test/test_descr.py

@@ -3306,6 +3306,16 @@ def testrmul():
     vereq(2*a, "rmul")
     vereq(2.2*a, "rmul")
 
+def testipow():
+    # [SF bug 620179]
+    if verbose:
+        print "Testing correct invocation of __ipow__..."
+    class C(object):
+        def __ipow__(self, other):
+            pass
+    a = C()
+    a **= 2
+
 def do_this_first():
     if verbose:
         print "Testing SF bug 551412 ..."
@@ -3401,6 +3411,7 @@ def test_main():
     slottrash()
     slotmultipleinheritance()
     testrmul()
+    testipow()
     if verbose: print "All OK"
 
 if __name__ == "__main__":

Objects/typeobject.c

@@ -3399,7 +3399,7 @@ SLOT1(slot_nb_inplace_subtract, "__isub__", PyObject *, "O")
 SLOT1(slot_nb_inplace_multiply, "__imul__", PyObject *, "O")
 SLOT1(slot_nb_inplace_divide, "__idiv__", PyObject *, "O")
 SLOT1(slot_nb_inplace_remainder, "__imod__", PyObject *, "O")
-SLOT2(slot_nb_inplace_power, "__ipow__", PyObject *, PyObject *, "OO")
+SLOT1(slot_nb_inplace_power, "__ipow__", PyObject *, "O")
 SLOT1(slot_nb_inplace_lshift, "__ilshift__", PyObject *, "O")
 SLOT1(slot_nb_inplace_rshift, "__irshift__", PyObject *, "O")
 SLOT1(slot_nb_inplace_and, "__iand__", PyObject *, "O")
@@ -4038,7 +4038,7 @@ static slotdef slotdefs[] = {
 	IBSLOT("__imod__", nb_inplace_remainder, slot_nb_inplace_remainder,
 	       wrap_binaryfunc, "%"),
 	IBSLOT("__ipow__", nb_inplace_power, slot_nb_inplace_power,
-	       wrap_ternaryfunc, "**"),
+	       wrap_binaryfunc, "**"),
 	IBSLOT("__ilshift__", nb_inplace_lshift, slot_nb_inplace_lshift,
 	       wrap_binaryfunc, "<<"),
 	IBSLOT("__irshift__", nb_inplace_rshift, slot_nb_inplace_rshift,