allow user_id to be filled if optional screen_name is included

twitter/api.py

@@ -2997,7 +2997,8 @@ def GetSentDirectMessages(self,
 
     def PostDirectMessage(self,
                           text,
-                          user_id,
+                          user_id=None,
+                          screen_name=None,
                           return_json=False):
         """Post a twitter direct message from the authenticated user.
 
@@ -3012,6 +3013,11 @@ def PostDirectMessage(self,
         """
         url = '%s/direct_messages/events/new.json' % self.base_url
 
+        # Hack to allow some sort of backwards compatibility with older versions
+        # part of the fix for Issue #587
+        if user_id is None and screen_name is not None:
+            user_id = self.GetUser(screen_name=screen_name).id
+
         event = {
             'event': {
                 'type': 'message_create',