BUG: fix array_namespace for NumPy scalars

Author: lucascolley

Diff for: array_api_compat/common/_helpers.py

@@ -342,7 +342,7 @@ def your_function(x, y):
             else:
                 # numpy 2.0 has __array_namespace__ and is fully array API
                 # compatible.
-                if hasattr(x, '__array_namespace__'):
+                if hasattr(np.empty(0), '__array_namespace__'):
                     namespaces.add(x.__array_namespace__(api_version=api_version))
                 else:
                     namespaces.add(numpy_namespace)

Diff for: tests/test_array_namespace.py

@@ -36,6 +36,13 @@ def test_array_namespace(library, api_version, use_compat):
         else:
             assert namespace == getattr(array_api_compat, library)
 
+    if library == "numpy":
+        # check that the same library is returned for NumPy scalars
+        scalar_namespace = array_api_compat.array_namespace(
+            xp.float64(0.0), api_version=api_version, use_compat=use_compat
+        )
+        assert scalar_namespace == namespace
+
     # Check that array_namespace works even if jax.experimental.array_api
     # hasn't been imported yet (it monkeypatches __array_namespace__
     # onto JAX arrays, but we should support them regardless). The only way to