revert NotImplemented return values in dot & others (scipy#22373)

Author: dschult

scipy/sparse/_base.py

@@ -685,7 +685,8 @@ def _matmul_dispatch(self, other):
 
             return result
 
-        return NotImplemented
+        else:
+            raise ValueError('could not interpret dimensions')
 
     def __mul__(self, other):
         return self.multiply(other)

scipy/sparse/_coo.py

@@ -866,10 +866,7 @@ def dot(self, other):
             o_array = np.asanyarray(other)
 
             if o_array.ndim == 0 and o_array.dtype == np.object_:
-                # Not interpretable as an array; return NotImplemented so that
-                # other's __rmatmul__ can kick in if that's implemented.
-                return NotImplemented
-
+                raise TypeError(f"dot argument not supported type: '{type(other)}'")
             try:
                 other.shape
             except AttributeError:
@@ -1082,9 +1079,7 @@ def tensordot(self, other, axes=2):
             other_array = np.asanyarray(other)
 
             if other_array.ndim == 0 and other_array.dtype == np.object_:
-                # Not interpretable as an array; return NotImplemented
-                return NotImplemented
-
+                raise TypeError(f"tensordot arg not supported type: '{type(other)}'")
             try:
                 other.shape
             except AttributeError:

scipy/sparse/tests/test_coo.py

@@ -719,6 +719,18 @@ def test_dot_with_inconsistent_shapes():
         arr_a.dot(arr_b)
 
 
+def test_matmul_dot_not_implemented():
+    arr_a = coo_array([[1, 2], [3, 4]])
+    with pytest.raises(TypeError, match="argument not supported type"):
+        arr_a.dot(None)
+    with pytest.raises(TypeError, match="arg not supported type"):
+        arr_a.tensordot(None)
+    with pytest.raises(TypeError, match="unsupported operand type"):
+        arr_a @ None
+    with pytest.raises(TypeError, match="unsupported operand type"):
+        None @ arr_a
+
+
 dot_shapes = [
     ((3,3), (3,3)), ((4,6), (6,7)), ((1,4), (4,1)), # matrix multiplication 2-D
     ((3,2,4,7), (7,)), ((5,), (6,3,5,2)), # dot of n-D and 1-D arrays