BUG: Fix 0-d array special case from reductions.

This channels scalars through the usual reduction machinery and
modifies it slightly to correctly support scalar reductions of
identity-less ufuncs.

3 files changed, 23 insertions, 24 deletions

diff --git a/numpy/core/src/umath/reduction.c b/numpy/core/src/umath/reduction.c
index f69aea2d0..3f2b94a4a 100644
--- a/numpy/core/src/umath/reduction.c
+++ b/numpy/core/src/umath/reduction.c
@@ -483,7 +483,8 @@ PyUFunc_ReduceWrapper(PyArrayObject *operand, PyArrayObject *out,
         if (op_view == NULL) {
             goto fail;
         }
-        if (PyArray_SIZE(op_view) == 0) {
+        /* empty op_view signals no reduction; but 0-d arrays cannot be empty */
+        if ((PyArray_SIZE(op_view) == 0) || (PyArray_NDIM(operand) == 0)) {
             Py_DECREF(op_view);
             op_view = NULL;
             goto finish;
diff --git a/numpy/core/src/umath/ufunc_object.c b/numpy/core/src/umath/ufunc_object.c
index 9c499d322..3d3f63d4e 100644
--- a/numpy/core/src/umath/ufunc_object.c
+++ b/numpy/core/src/umath/ufunc_object.c
@@ -3684,31 +3684,16 @@ PyUFunc_GenericReduction(PyUFuncObject *ufunc, PyObject *args,
          * 'prod', et al, also allow a reduction where axis=0, even
          * though this is technically incorrect.
          */
-        if (operation == UFUNC_REDUCE &&
-                    (naxes == 0 || (naxes == 1 && axes[0] == 0))) {
+        naxes = 0;
+
+        if (!(operation == UFUNC_REDUCE &&
+                    (naxes == 0 || (naxes == 1 && axes[0] == 0)))) {
+            PyErr_Format(PyExc_TypeError, "cannot %s on a scalar",
+                         _reduce_type[operation]);
             Py_XDECREF(otype);
-            /* If there's an output parameter, copy the value */
-            if (out != NULL) {
-                if (PyArray_CopyInto(out, mp) < 0) {
-                    Py_DECREF(mp);
-                    return NULL;
-                }
-                else {
-                    Py_DECREF(mp);
-                    Py_INCREF(out);
-                    return (PyObject *)out;
-                }
-            }
-            /* Otherwise return the array unscathed */
-            else {
-                return PyArray_Return(mp);
-            }
+            Py_DECREF(mp);
+            return NULL;
         }
-        PyErr_Format(PyExc_TypeError, "cannot %s on a scalar",
-                     _reduce_type[operation]);
-        Py_XDECREF(otype);
-        Py_DECREF(mp);
-        return NULL;
     }
 
      /*
diff --git a/numpy/core/tests/test_ufunc.py b/numpy/core/tests/test_ufunc.py
index dbbd15397..816b22052 100644
--- a/numpy/core/tests/test_ufunc.py
+++ b/numpy/core/tests/test_ufunc.py
@@ -564,12 +564,25 @@ class TestUfunc(TestCase):
         assert_equal(np.max(3, axis=0), 3)
         assert_equal(np.min(2.5, axis=0), 2.5)
 
+        # Check scalar behaviour for ufuncs without an identity
+        assert_equal(np.power.reduce(3), 3)
+
         # Make sure that scalars are coming out from this operation
         assert_(type(np.prod(np.float32(2.5), axis=0)) is np.float32)
         assert_(type(np.sum(np.float32(2.5), axis=0)) is np.float32)
         assert_(type(np.max(np.float32(2.5), axis=0)) is np.float32)
         assert_(type(np.min(np.float32(2.5), axis=0)) is np.float32)
 
+        # check if scalars/0-d arrays get cast
+        assert_(type(np.any(0, axis=0)) is np.bool_)
+
+        # assert that 0-d arrays get wrapped
+        class MyArray(np.ndarray):
+            pass
+        a = np.array(1).view(MyArray)
+        assert_(type(np.any(a)) is MyArray)
+
+
     def test_casting_out_param(self):
         # Test that it's possible to do casts on output
         a = np.ones((200,100), np.int64)