numpy · charris · May 27, 2018 · Feb 17, 2018 · May 26, 2018
diff --git a/doc/release/1.15.0-notes.rst b/doc/release/1.15.0-notes.rst
@@ -46,6 +46,13 @@ Deprecations
   * `np.ma.load`, `np.ma.dump` - these functions already failed on python 3,
     when called with a string.
 
+* Multidimensional indexing with anything but a tuple is
+  deprecated. This means that code such as ``ind = [slice(None), 0]``,
+  ``arr[[slice(None), 0]]`` should be changed to ``arr[tuple(ind)]``. This is
+  necessary to avoid ambiguity in expressions such as ``arr[[[0, 1], [0, 1]]]``
+  which currently is interpreted as ``arr[array([0, 1]), array([0, 1])]``.
+  In future, this will be interpreted as ``arr[array([[0, 1], [0, 1]])]``.
+
 * Direct imports from the following modules is deprecated. All testing related
   imports should come from `numpy.testing`.
   * `np.testing.utils`

diff --git a/doc/source/reference/arrays.indexing.rst b/doc/source/reference/arrays.indexing.rst
@@ -29,11 +29,15 @@ dimensions. Basic slicing occurs when *obj* is a :class:`slice` object
 (constructed by ``start:stop:step`` notation inside of brackets), an
 integer, or a tuple of slice objects and integers. :const:`Ellipsis`
 and :const:`newaxis` objects can be interspersed with these as
-well. In order to remain backward compatible with a common usage in
-Numeric, basic slicing is also initiated if the selection object is
-any non-ndarray sequence (such as a :class:`list`) containing :class:`slice`
-objects, the :const:`Ellipsis` object, or the :const:`newaxis` object,
-but not for integer arrays or other embedded sequences.
+well.
+
+.. deprecated:: 1.15.0
+
+  In order to remain backward compatible with a common usage in
+  Numeric, basic slicing is also initiated if the selection object is
+  any non-ndarray and non-tuple sequence (such as a :class:`list`) containing
+  :class:`slice` objects, the :const:`Ellipsis` object, or the :const:`newaxis`
+  object, but not for integer arrays or other embedded sequences.
 
 .. index::
    triple: ndarray; special methods; getitem
@@ -196,7 +200,8 @@ basic slicing that returns a :term:`view`).
    why this occurs.
 
    Also recognize that ``x[[1,2,3]]`` will trigger advanced indexing,
-   whereas ``x[[1,2,slice(None)]]`` will trigger basic slicing.
+   whereas due to the deprecated Numeric compatibility mentioned above,
+   ``x[[1,2,slice(None)]]`` will trigger basic slicing.
 
 Integer array indexing
 ^^^^^^^^^^^^^^^^^^^^^^

diff --git a/numpy/core/src/multiarray/mapping.c b/numpy/core/src/multiarray/mapping.c
@@ -293,8 +293,7 @@ unpack_indices(PyObject *index, PyObject **result, npy_intp result_n)
         if (commit_to_unpack) {
             /* propagate errors */
             if (tmp_obj == NULL) {
-                multi_DECREF(result, i);
-                return -1;
+                goto fail;
             }
         }
         else {
@@ -313,6 +312,16 @@ unpack_indices(PyObject *index, PyObject **result, npy_intp result_n)
                     || PySlice_Check(tmp_obj)
                     || tmp_obj == Py_Ellipsis
                     || tmp_obj == Py_None) {
+                if (DEPRECATE_FUTUREWARNING(
+                        "Using a non-tuple sequence for multidimensional "
+                        "indexing is deprecated; use `arr[tuple(seq)]` "
+                        "instead of `arr[seq]`. In the future this will be "
+                        "interpreted as an array index, `arr[np.array(seq)]`, "
+                        "which will result either in an error or a different "
+                        "result.") < 0) {
+                    i++;  /* since loop update doesn't run */
+                    goto fail;
+                }
                 commit_to_unpack = 1;
             }
         }
@@ -328,6 +337,10 @@ unpack_indices(PyObject *index, PyObject **result, npy_intp result_n)
         multi_DECREF(result, i);
         return unpack_scalar(index, result, result_n);
     }
+
+fail:
+    multi_DECREF(result, i);
+    return -1;
 }
 
 /**

diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
@@ -134,6 +134,22 @@ class _VisibleDeprecationTestCase(_DeprecationTestCase):
     warning_cls = np.VisibleDeprecationWarning
 
 
+class TestNonTupleNDIndexDeprecation(object):
+    def test_basic(self):
+        a = np.zeros((5, 5))
+        with warnings.catch_warnings():
+            warnings.filterwarnings('always')
+            assert_warns(FutureWarning, a.__getitem__, [[0, 1], [0, 1]])
+            assert_warns(FutureWarning, a.__getitem__, [slice(None)])
+
+            warnings.filterwarnings('error')
+            assert_raises(FutureWarning, a.__getitem__, [[0, 1], [0, 1]])
+            assert_raises(FutureWarning, a.__getitem__, [slice(None)])
+
+            # a a[[0, 1]] always was advanced indexing, so no error/warning
+            a[[0, 1]]
+
+
 class TestRankDeprecation(_DeprecationTestCase):
     """Test that np.rank is deprecated. The function should simply be
     removed. The VisibleDeprecationWarning may become unnecessary.