fix self.excess_draggables

common/lib/capa/capa/verifiers/draganddrop.py

@@ -353,7 +353,7 @@ class DragAndDrop(object):
         # correct_answer entry, the value is False.
         # default to consider every user answer excess until proven otherwise.
         self.excess_draggables = dict((users_draggable.keys()[0],True)
-            for users_draggable in user_answer['draggables'])
+            for users_draggable in user_answer)
 
         # Convert nested `user_answer` to flat format.
         user_answer = flat_user_answer(user_answer)