SF patch #1390657:

* set sq_repeat and sq_concat to NULL for user-defined new-style
  classes, as a way to fix a number of related problems.  See
  test_descr.notimplemented()).  One of these problems was fixed
  in r25556 and r25557 but many more existed; this is a general
  fix and thus reverts r25556-r25557.

* to avoid having PySequence_Repeat()/PySequence_Concat() failing
  on user-defined classes, they now fall back to nb_add/nb_mul if
  sq_concat/sq_repeat are not defined and the arguments appear to
  be sequences.

* added tests.

Backport candidate.

1 files changed, 45 insertions, 6 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 1f8feb5..6e070a9 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -635,14 +635,11 @@ PyNumber_Add(PyObject *v, PyObject *w)
 	PyObject *result = binary_op1(v, w, NB_SLOT(nb_add));
 	if (result == Py_NotImplemented) {
 		PySequenceMethods *m = v->ob_type->tp_as_sequence;
+		Py_DECREF(result);
 		if (m && m->sq_concat) {
-			Py_DECREF(result);
-			result = (*m->sq_concat)(v, w);
+			return (*m->sq_concat)(v, w);
 		}
-		if (result == Py_NotImplemented) {
-			Py_DECREF(result);
-			return binop_type_error(v, w, "+");
-                }
+		result = binop_type_error(v, w, "+");
 	}
 	return result;
 }
@@ -1144,6 +1141,15 @@ PySequence_Concat(PyObject *s, PyObject *o)
 	if (m && m->sq_concat)
 		return m->sq_concat(s, o);
 
+	/* Instances of user classes defining an __add__() method only
+	   have an nb_add slot, not an sq_concat slot.  So we fall back
+	   to nb_add if both arguments appear to be sequences. */
+	if (PySequence_Check(s) && PySequence_Check(o)) {
+		PyObject *result = binary_op1(s, o, NB_SLOT(nb_add));
+		if (result != Py_NotImplemented)
+			return result;
+		Py_DECREF(result);
+	}
 	return type_error("object can't be concatenated");
 }
 
@@ -1159,6 +1165,20 @@ PySequence_Repeat(PyObject *o, int count)
 	if (m && m->sq_repeat)
 		return m->sq_repeat(o, count);
 
+	/* Instances of user classes defining a __mul__() method only
+	   have an nb_multiply slot, not an sq_repeat slot. so we fall back
+	   to nb_multiply if o appears to be a sequence. */
+	if (PySequence_Check(o)) {
+		PyObject *n, *result;
+		n = PyInt_FromLong(count);
+		if (n == NULL)
+			return NULL;
+		result = binary_op1(o, n, NB_SLOT(nb_multiply));
+		Py_DECREF(n);
+		if (result != Py_NotImplemented)
+			return result;
+		Py_DECREF(result);
+	}
 	return type_error("object can't be repeated");
 }
 
@@ -1176,6 +1196,13 @@ PySequence_InPlaceConcat(PyObject *s, PyObject *o)
 	if (m && m->sq_concat)
 		return m->sq_concat(s, o);
 
+	if (PySequence_Check(s) && PySequence_Check(o)) {
+		PyObject *result = binary_iop1(s, o, NB_SLOT(nb_inplace_add),
+					       NB_SLOT(nb_add));
+		if (result != Py_NotImplemented)
+			return result;
+		Py_DECREF(result);
+	}
 	return type_error("object can't be concatenated");
 }
 
@@ -1193,6 +1220,18 @@ PySequence_InPlaceRepeat(PyObject *o, int count)
 	if (m && m->sq_repeat)
 		return m->sq_repeat(o, count);
 
+	if (PySequence_Check(o)) {
+		PyObject *n, *result;
+		n = PyInt_FromLong(count);
+		if (n == NULL)
+			return NULL;
+		result = binary_iop1(o, n, NB_SLOT(nb_inplace_multiply),
+				     NB_SLOT(nb_multiply));
+		Py_DECREF(n);
+		if (result != Py_NotImplemented)
+			return result;
+		Py_DECREF(result);
+	}
 	return type_error("object can't be repeated");
 }