Update devito/ir/clusters/visitors.py

Co-authored-by: Ed Caunt <[email protected]>

Author: JDBetteridge

devito/ir/clusters/visitors.py

@@ -141,7 +141,7 @@ def __new__(cls, *args, mode='dense'):
             elif len(args) == 2:
                 func, mode = args
             else:
-                raise AssertionError('Too many args')
+                raise ValueError(f"Either 1 or 2 arguments permitted, {len(args)} provided")
             obj = object.__new__(cls)
             obj.__init__(func, mode)
             return obj