DEP: Warn when using bool.__index__, rather than removing it completely

2 files changed, 9 insertions, 4 deletions

diff --git a/numpy/core/src/multiarray/scalartypes.c.src b/numpy/core/src/multiarray/scalartypes.c.src
index 1c809f409..7ccdd579a 100644
--- a/numpy/core/src/multiarray/scalartypes.c.src
+++ b/numpy/core/src/multiarray/scalartypes.c.src
@@ -2843,9 +2843,14 @@ static PyNumberMethods @name@_arrtype_as_number;
 static PyObject *
 bool_index(PyObject *a)
 {
-    PyErr_SetString(PyExc_TypeError, 
-                    "A boolean scalar cannot be converted to an index");
-    return NULL;
+    if (DEPRECATE(
+            "In future, it will be an error for 'np.bool_' scalars to be "
+            "interpreted as an index") < 0) {
+        return NULL;
+    }
+    else {
+        return PyInt_FromLong(PyArrayScalar_VAL(a, Bool));
+    }
 }
 
 /* Arithmetic methods -- only so we can override &, |, ^. */
diff --git a/numpy/core/tests/test_indexing.py b/numpy/core/tests/test_indexing.py
index 9259bb9d4..7cfb81da7 100644
--- a/numpy/core/tests/test_indexing.py
+++ b/numpy/core/tests/test_indexing.py
@@ -1174,7 +1174,7 @@ class TestBooleanIndexing(object):
         # Note that operator.index(np.array(True)) does not work, a boolean
         # array is thus also deprecated, but not with the same message:
         assert_raises(TypeError, operator.index, np.array(True))
-        assert_raises(TypeError, operator.index, np.True_)
+        assert_warns(DeprecationWarning, operator.index, np.True_)
         assert_raises(TypeError, np.take, args=(a, [0], False))
 
     def test_boolean_indexing_weirdness(self):