numpy · charris · Mar 25, 2016 · Mar 20, 2016 · charris · Mar 24, 2016
diff --git a/numpy/core/src/multiarray/scalartypes.c.src b/numpy/core/src/multiarray/scalartypes.c.src
@@ -264,10 +264,20 @@ gentype_@name@(PyObject *m1, PyObject *m2)
 static PyObject *
 gentype_multiply(PyObject *m1, PyObject *m2)
 {
-    PyObject *ret = NULL;
     npy_intp repeat;
 
+    /*
+     * If the other object supports sequence repeat and not number multiply
+     * we should call sequence repeat to support e.g. list repeat by numpy
+     * scalars (they may be converted to ndarray otherwise).
+     * A python defined class will always only have the nb_multiply slot and
+     * some classes may have neither defined. For the latter we want need
+     * to give the normal case a chance to convert the object to ndarray.
+     * Probably no class has both defined, but if they do, prefer number.
+     */
     if (!PyArray_IsScalar(m1, Generic) &&
+            ((Py_TYPE(m1)->tp_as_sequence != NULL) &&
+             (Py_TYPE(m1)->tp_as_sequence->sq_repeat != NULL)) &&
             ((Py_TYPE(m1)->tp_as_number == NULL) ||
              (Py_TYPE(m1)->tp_as_number->nb_multiply == NULL))) {
         /* Try to convert m2 to an int and try sequence repeat */
@@ -276,23 +286,23 @@ gentype_multiply(PyObject *m1, PyObject *m2)
             return NULL;
         }
         /* Note that npy_intp is compatible to Py_Ssize_t */
-        ret = PySequence_Repeat(m1, repeat);
+        return PySequence_Repeat(m1, repeat);
     }
-    else if (!PyArray_IsScalar(m2, Generic) &&
+    if (!PyArray_IsScalar(m2, Generic) &&
+            ((Py_TYPE(m2)->tp_as_sequence != NULL) &&
+             (Py_TYPE(m2)->tp_as_sequence->sq_repeat != NULL)) &&
             ((Py_TYPE(m2)->tp_as_number == NULL) ||
              (Py_TYPE(m2)->tp_as_number->nb_multiply == NULL))) {
         /* Try to convert m1 to an int and try sequence repeat */
         repeat = PyArray_PyIntAsIntp(m1);
         if (repeat == -1 && PyErr_Occurred()) {
             return NULL;
         }
-        ret = PySequence_Repeat(m2, repeat);
-    }
-    if (ret == NULL) {
-        PyErr_Clear(); /* no effect if not set */
-        ret = PyArray_Type.tp_as_number->nb_multiply(m1, m2);
+        return PySequence_Repeat(m2, repeat);
     }
-    return ret;
+
+    /* All normal cases are handled by PyArray's multiply */
+    return PyArray_Type.tp_as_number->nb_multiply(m1, m2);
 }
 
 /**begin repeat

diff --git a/numpy/core/tests/test_scalarmath.py b/numpy/core/tests/test_scalarmath.py
@@ -9,7 +9,7 @@
 from numpy.testing.utils import _gen_alignment_data
 from numpy.testing import (
     TestCase, run_module_suite, assert_, assert_equal, assert_raises,
-    assert_almost_equal, assert_allclose
+    assert_almost_equal, assert_allclose, assert_array_equal
 )
 
 types = [np.bool_, np.byte, np.ubyte, np.short, np.ushort, np.intc, np.uintc,
@@ -448,6 +448,44 @@ def test_error(self):
         assert_raises(TypeError, d.__sizeof__, "a")
 
 
+class TestMultiply(TestCase):
+    def test_seq_repeat(self):
+        # Test that basic sequences get repeated when multiplied with
+        # numpy integers. And errors are raised when multiplied with others.
+        # Some of this behaviour may be controversial and could be open for
+        # change.
+        for seq_type in (list, tuple):
+            seq = seq_type([1, 2, 3])
+            for numpy_type in np.typecodes["AllInteger"]:
+                i = np.dtype(numpy_type).type(2)
+                assert_equal(seq * i, seq * int(i))
+                assert_equal(i * seq, int(i) * seq)
+
+            for numpy_type in np.typecodes["All"].replace("V", ""):
+                if numpy_type in np.typecodes["AllInteger"]:
+                    continue
+                i = np.dtype(numpy_type).type()
+                assert_raises(TypeError, operator.mul, seq, i)
+                assert_raises(TypeError, operator.mul, i, seq)
+
+    def test_no_seq_repeat_basic_array_like(self):
+        # Test that an array-like which does not know how to be multiplied
+        # does not attempt sequence repeat (raise TypeError).
+        # See also gh-7428.
+        class ArrayLike(object):
+            def __init__(self, arr):
+                self.arr = arr
+            def __array__(self):
+                return self.arr
+
+        # Test for simple ArrayLike above and memoryviews (original report)
+        for arr_like in (ArrayLike(np.ones(3)), memoryview(np.ones(3))):
+            assert_array_equal(arr_like * np.float32(3.), np.full(3, 3.))
+            assert_array_equal(np.float32(3.) * arr_like, np.full(3, 3.))
+            assert_array_equal(arr_like * np.int_(3), np.full(3, 3))
+            assert_array_equal(np.int_(3) * arr_like, np.full(3, 3))
+
+
 class TestAbs(TestCase):
 
     def _test_abs_func(self, absfunc):