From b5de219d1ed6d5a739843bd155f7fd9bd85c26ca Mon Sep 17 00:00:00 2001
From: Stephan Hoyer <shoyer@google.com>
Date: Thu, 27 Apr 2017 08:45:43 -0700
Subject: [PATCH 1/2] bpo-30140: Fix binary operator dispatch for subclasses

---
 Lib/test/test_binop.py | 34 +++++++++++++++++++++++++++++++++-
 Lib/test/test_descr.py | 12 ------------
 Objects/typeobject.c   | 38 +-------------------------------------
 3 files changed, 34 insertions(+), 50 deletions(-)

diff --git a/Lib/test/test_binop.py b/Lib/test/test_binop.py
index 4f5b8a8b93ed47..842aa7283b1f6e 100644
--- a/Lib/test/test_binop.py
+++ b/Lib/test/test_binop.py
@@ -1,7 +1,7 @@
 """Tests for binary operators on subtypes of built-in types."""
 
 import unittest
-from operator import eq, le, ne
+from operator import eq, le, ne, add
 from abc import ABCMeta
 
 def gcd(a, b):
@@ -387,6 +387,38 @@ def test_comparison_orders(self):
         self.assertEqual(op_sequence(eq, B, V), ['B.__eq__', 'V.__eq__'])
         self.assertEqual(op_sequence(le, B, V), ['B.__le__', 'V.__ge__'])
 
+    def test_arithmetic_orders(self):
+
+        def logged_op(name):
+            def op(self, other):
+                type_name = type(self).__name__
+                self.log_operation(f'{type_name}.__{name}__')
+                return NotImplemented
+            return op
+
+        class A(OperationLogger):
+            __add__ = logged_op('add')
+            __radd__ = logged_op('radd')
+
+        class B(OperationLogger):
+            __add__ = logged_op('add')
+            __radd__ = logged_op('radd')
+
+        class C(A):
+            pass
+
+        class D(OperationLogger):
+            pass
+
+        self.assertEqual(op_sequence(add, A, A), ['A.__add__'])
+        self.assertEqual(op_sequence(add, A, D), ['A.__add__'])
+        self.assertEqual(op_sequence(add, D, A), ['A.__radd__'])
+        self.assertEqual(op_sequence(add, A, B), ['A.__add__', 'B.__radd__'])
+        self.assertEqual(op_sequence(add, B, A), ['B.__add__', 'A.__radd__'])
+        self.assertEqual(op_sequence(add, A, C), ['C.__radd__', 'A.__add__'])
+        self.assertEqual(op_sequence(add, C, A), ['C.__add__', 'A.__radd__'])
+
+
 class SupEq(object):
     """Class that can test equality"""
     def __eq__(self, other):
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index ced25f3fc44244..afa37f08b5c7f0 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -4111,18 +4111,6 @@ def __rfloordiv__(self, other):
         self.assertEqual(D() // C(), "D.__floordiv__")
         self.assertEqual(C() // D(), "D.__rfloordiv__")
 
-        # Case 4: this didn't work right in 2.2.2 and 2.3a1
-
-        class E(C):
-            pass
-
-        self.assertEqual(E.__rfloordiv__, C.__rfloordiv__)
-
-        self.assertEqual(E() // 1, "C.__floordiv__")
-        self.assertEqual(1 // E(), "C.__rfloordiv__")
-        self.assertEqual(E() // C(), "C.__floordiv__")
-        self.assertEqual(C() // E(), "C.__floordiv__") # This one would fail
-
     @support.impl_detail("testing an internal kind of method object")
     def test_meth_class_get(self):
         # Testing __get__ method of METH_CLASS C methods...
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 9eb725f062ba56..fdf0584323cbfd 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -5841,41 +5841,6 @@ FUNCNAME(PyObject *self, ARG1TYPE arg1) \
     return call_method(self, &id, stack, 1); \
 }
 
-/* Boolean helper for SLOT1BINFULL().
-   right.__class__ is a nontrivial subclass of left.__class__. */
-static int
-method_is_overloaded(PyObject *left, PyObject *right, struct _Py_Identifier *name)
-{
-    PyObject *a, *b;
-    int ok;
-
-    b = _PyObject_GetAttrId((PyObject *)(Py_TYPE(right)), name);
-    if (b == NULL) {
-        PyErr_Clear();
-        /* If right doesn't have it, it's not overloaded */
-        return 0;
-    }
-
-    a = _PyObject_GetAttrId((PyObject *)(Py_TYPE(left)), name);
-    if (a == NULL) {
-        PyErr_Clear();
-        Py_DECREF(b);
-        /* If right has it but left doesn't, it's overloaded */
-        return 1;
-    }
-
-    ok = PyObject_RichCompareBool(a, b, Py_NE);
-    Py_DECREF(a);
-    Py_DECREF(b);
-    if (ok < 0) {
-        PyErr_Clear();
-        return 0;
-    }
-
-    return ok;
-}
-
-
 #define SLOT1BINFULL(FUNCNAME, TESTFUNC, SLOTNAME, OPSTR, ROPSTR) \
 static PyObject * \
 FUNCNAME(PyObject *self, PyObject *other) \
@@ -5890,8 +5855,7 @@ FUNCNAME(PyObject *self, PyObject *other) \
         Py_TYPE(self)->tp_as_number->SLOTNAME == TESTFUNC) { \
         PyObject *r; \
         if (do_other && \
-            PyType_IsSubtype(Py_TYPE(other), Py_TYPE(self)) && \
-            method_is_overloaded(self, other, &rop_id)) { \
+            PyType_IsSubtype(Py_TYPE(other), Py_TYPE(self))) { \
             stack[0] = self; \
             r = call_maybe(other, &rop_id, stack, 1); \
             if (r != Py_NotImplemented) \

From 52d67e8489b6bd2cc8466372528cfef6f04d5f8a Mon Sep 17 00:00:00 2001
From: Stephan Hoyer <shoyer@google.com>
Date: Tue, 5 Sep 2017 14:55:07 -0700
Subject: [PATCH 2/2] bpo-30140: Add blurb

---
 .../Core and Builtins/2017-09-05-14-54-30.bpo-30140.fnPWpS.rst  | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2017-09-05-14-54-30.bpo-30140.fnPWpS.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-09-05-14-54-30.bpo-30140.fnPWpS.rst b/Misc/NEWS.d/next/Core and Builtins/2017-09-05-14-54-30.bpo-30140.fnPWpS.rst
new file mode 100644
index 00000000000000..9f570815e890bb
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2017-09-05-14-54-30.bpo-30140.fnPWpS.rst	
@@ -0,0 +1,2 @@
+Fix binary operator dispatch to try subclasses implementations first always,
+even if the subclass does not directly override the relevant special method.