More py3 fixes, bring back py2 compat

arachnado/rpc/__init__.py

@@ -28,7 +28,7 @@ def handle_request(self, body):
         else:
             self.send_data(response.data)
 
-    def on_done(self, future, *, data):
+    def on_done(self, future, data):
         data['result'] = future.result()
         self.send_data(data)
 

arachnado/storages/mongotail.py

@@ -1,4 +1,4 @@
-import pymongo
+import six
 from bson.objectid import ObjectId
 from tornado.gen import sleep, coroutine
 
@@ -28,7 +28,7 @@ def tail(self, query=None, fields=None, last_object_id=None):
         if self.tailing:
             raise RuntimeError('This storage is already tailing')
         self.tailing = True
-        if isinstance(last_object_id, basestring):
+        if isinstance(last_object_id, six.string_types):
             last_object_id = ObjectId(last_object_id)
 
         if query is not None:
@@ -76,7 +76,8 @@ def _objectify(self, query):
                     stack.append(v)
                 elif isinstance(v, list):
                     stack.extend(v)
-                elif isinstance(v, unicode) and v.startswith(u'ObjectId('):
+                elif isinstance(v, six.string_types) \
+                        and v.startswith(u'ObjectId('):
                     d[k] = ObjectId(v[9:-1])
 
         return query