Support calling positional arguments by keyword (fix #998) (#2081)

test/actor_test.py

@@ -57,6 +57,9 @@ class ActorAPI(unittest.TestCase):
         self.assertEqual(
             ray.get(actor.get_values.remote(0, arg2="d", arg1=0)),
             (1, 2, "cd"))
+        self.assertEqual(
+            ray.get(actor.get_values.remote(arg2="d", arg1=0, arg0=2)),
+            (3, 2, "cd"))
 
         # Make sure we get an exception if the constructor is called
         # incorrectly.
@@ -66,6 +69,9 @@ class ActorAPI(unittest.TestCase):
         with self.assertRaises(Exception):
             actor = Actor.remote(0, 1, 2, arg3=3)
 
+        with self.assertRaises(Exception):
+            actor = Actor.remote(0, arg0=1)
+
         # Make sure we get an exception if the method is called incorrectly.
         actor = Actor.remote(1)
         with self.assertRaises(Exception):