Merge pull request #9884 from eric-wieser/unravel_index-0d

BUG: Allow `unravel_index(0, ())` to return ()

2 files changed, 36 insertions, 11 deletions

diff --git a/numpy/core/src/multiarray/compiled_base.c b/numpy/core/src/multiarray/compiled_base.c
index 36ef1d1c4..580578562 100644
--- a/numpy/core/src/multiarray/compiled_base.c
+++ b/numpy/core/src/multiarray/compiled_base.c
@@ -1135,8 +1135,11 @@ unravel_index_loop_corder(int unravel_ndim, npy_intp *unravel_dims,
     }
     NPY_END_ALLOW_THREADS;
     if (invalid) {
-        PyErr_SetString(PyExc_ValueError,
-              "invalid entry in index array");
+        PyErr_Format(PyExc_ValueError,
+            "index %" NPY_INTP_FMT " is out of bounds for array with size "
+            "%" NPY_INTP_FMT,
+            val, unravel_size
+        );
         return NPY_FAIL;
     }
     return NPY_SUCCEED;
@@ -1169,8 +1172,11 @@ unravel_index_loop_forder(int unravel_ndim, npy_intp *unravel_dims,
     }
     NPY_END_ALLOW_THREADS;
     if (invalid) {
-        PyErr_SetString(PyExc_ValueError,
-              "invalid entry in index array");
+        PyErr_Format(PyExc_ValueError,
+            "index %" NPY_INTP_FMT " is out of bounds for array with size "
+            "%" NPY_INTP_FMT,
+            val, unravel_size
+        );
         return NPY_FAIL;
     }
     return NPY_SUCCEED;
@@ -1202,12 +1208,6 @@ arr_unravel_index(PyObject *self, PyObject *args, PyObject *kwds)
         goto fail;
     }
 
-    if (dimensions.len == 0) {
-        PyErr_SetString(PyExc_ValueError,
-                "dims must have at least one value");
-        goto fail;
-    }
-
     unravel_size = PyArray_MultiplyList(dimensions.ptr, dimensions.len);
 
     if (!PyArray_Check(indices0)) {
@@ -1328,6 +1328,20 @@ arr_unravel_index(PyObject *self, PyObject *args, PyObject *kwds)
         goto fail;
     }
 
+
+    if (dimensions.len == 0 && PyArray_NDIM(indices) != 0) {
+        /*
+         * There's no index meaning "take the only element 10 times"
+         * on a zero-d array, so we have no choice but to error. (See gh-580)
+         *
+         * Do this check after iterating, so we give a better error message
+         * for invalid indices.
+         */
+        PyErr_SetString(PyExc_ValueError,
+                "multiple indices are not supported for 0d arrays");
+        goto fail;
+    }
+
     /* Now make a tuple of views, one per index */
     ret_tuple = PyTuple_New(dimensions.len);
     if (ret_tuple == NULL) {
diff --git a/numpy/lib/tests/test_index_tricks.py b/numpy/lib/tests/test_index_tricks.py
index 452b3d6a2..1d5efef86 100644
--- a/numpy/lib/tests/test_index_tricks.py
+++ b/numpy/lib/tests/test_index_tricks.py
@@ -3,7 +3,8 @@ from __future__ import division, absolute_import, print_function
 import numpy as np
 from numpy.testing import (
     run_module_suite, assert_, assert_equal, assert_array_equal,
-    assert_almost_equal, assert_array_almost_equal, assert_raises
+    assert_almost_equal, assert_array_almost_equal, assert_raises,
+    assert_raises_regex
     )
 from numpy.lib.index_tricks import (
     mgrid, ndenumerate, fill_diagonal, diag_indices, diag_indices_from,
@@ -114,6 +115,16 @@ class TestRavelUnravelIndex(object):
         assert_(y.flags.writeable)
 
 
+    def test_0d(self):
+        # gh-580
+        x = np.unravel_index(0, ())
+        assert_equal(x, ())
+
+        assert_raises_regex(ValueError, "0d array", np.unravel_index, [0], ())
+        assert_raises_regex(
+            ValueError, "out of bounds", np.unravel_index, [1], ())
+
+
 class TestGrid(object):
     def test_basic(self):
         a = mgrid[-1:1:10j]