Require that one of x1,x2 arguments to where is an array

array_api_strict/_searching_functions.py

@@ -90,18 +90,29 @@ def searchsorted(
     # x1 must be 1-D, but NumPy already requires this.
     return Array._new(np.searchsorted(x1._array, x2._array, side=side, sorter=sorter), device=x1.device)
 
-def where(condition: Array, x1: bool | int | float | Array, x2: bool | int | float | Array, /) -> Array:
+def where(
+    condition: Array,
+    x1: bool | int | float | complex | Array,
+    x2: bool | int | float | complex | Array, /
+) -> Array:
     """
     Array API compatible wrapper for :py:func:`np.where <numpy.where>`.
 
     See its docstring for more information.
     """
     if get_array_api_strict_flags()['api_version'] > '2023.12':
-        if isinstance(x1, (bool, float, int)):
+        num_scalars = 0
+
+        if isinstance(x1, (bool, float, complex, int)):
             x1 = Array._new(np.asarray(x1), device=condition.device)
+            num_scalars += 1
 
-        if isinstance(x2, (bool, float, int)):
+        if isinstance(x2, (bool, float, complex, int)):
             x2 = Array._new(np.asarray(x2), device=condition.device)
+            num_scalars += 1
+
+        if num_scalars == 2:
+            raise ValueError("One of x1, x2 arguments must be an array.")
 
     # Call result type here just to raise on disallowed type combinations
     _result_type(x1.dtype, x2.dtype)

array_api_strict/tests/test_searching_functions.py

@@ -20,7 +20,11 @@ def test_where_with_scalars():
           ),
           ArrayAPIStrictFlags(api_version=draft_version),
         ):
-        x_where = xp.where(x == 1, 42, 44)
+        x_where = xp.where(x == 1, xp.asarray(42), 44)
 
         expected = xp.asarray([42, 44, 44, 42])
         assert xp.all(x_where == expected)
+
+        # The spec does not allow both x1 and x2 to be scalars
+        with pytest.raises(ValueError, match="One of"):
+            xp.where(x == 1, 42, 44)