ENH: fancy indexing __setitem__ is not allowed

Author: ev-br

array_api_strict/_array_object.py

@@ -321,7 +321,7 @@ def _normalize_two_args(x1, x2) -> Tuple[Array, Array]:
 
     # Note: A large fraction of allowed indices are disallowed here (see the
     # docstring below)
-    def _validate_index(self, key):
+    def _validate_index(self, key, op="getitem"):
         """
         Validate an index according to the array API.
 
@@ -384,6 +384,9 @@ def _validate_index(self, key):
                     "zero-dimensional integer arrays and boolean arrays "
                     "are specified in the Array API."
                 )
+            if op == "setitem":
+                if isinstance(i, Array) and i.dtype in _integer_dtypes:
+                    raise IndexError("Fancy indexing __setitem__ is not supported.")
 
         nonexpanding_key = []
         single_axes = []
@@ -908,7 +911,7 @@ def __setitem__(
         """
         # Note: Only indices required by the spec are allowed. See the
         # docstring of _validate_index
-        self._validate_index(key)
+        self._validate_index(key, op="setitem")
         if isinstance(key, Array):
             # Indexing self._array with array_api_strict arrays can be erroneous
             key = key._array

array_api_strict/tests/test_array_object.py

@@ -117,9 +117,9 @@ def test_indexing_arrays():
     a_idx_loop = asarray([a[idx[i]] for i in range(idx.shape[0])])
     assert all(a_idx == a_idx_loop)
 
-    # setitem with arrays is not allowed      # XXX
-    # with assert_raises(IndexError):
-    #    a[idx] = 42
+    # setitem with arrays is not allowed
+    with assert_raises(IndexError):
+        a[idx] = 42
 
     # mixed array and integer indexing
     a = reshape(arange(3*4), (3, 4))
@@ -129,12 +129,15 @@ def test_indexing_arrays():
     a_idx_loop = asarray([a[idx[i], 1] for i in range(idx.shape[0])])
     assert all(a_idx == a_idx_loop)
 
-
     # index with two arrays
     a_idx = a[idx, idx]
     a_idx_loop = asarray([a[idx[i], idx[i]] for i in range(idx.shape[0])])
     assert all(a_idx == a_idx_loop)
 
+    # setitem with arrays is not allowed
+    with assert_raises(IndexError):
+        a[idx, idx] = 42
+
 
 def test_promoted_scalar_inherits_device():
     device1 = Device("device1")