bug fix: NameError when modify policies are returned

Author: ngsrinivas

pyretic/core/classifier.py

@@ -107,7 +107,7 @@ def __add__(self,c2):
     # Helper function for rshift: given a test b and an action p, return a test
     # b' such that p >> b == b' >> p.
     def _commute_test(self, act, pkts):
-        from pyretic.core.language import drop, identity, Controller, CountBucket, DerivedPolicy
+        from pyretic.core.language import modify, drop, identity, Controller, CountBucket, DerivedPolicy
         while isinstance(act, DerivedPolicy):
             act = act.policy
         if act == identity:
@@ -140,7 +140,7 @@ def _commute_test(self, act, pkts):
     # Helper function for rshift: sequentially compose actions.  a1 must be a
     # single action.  Returns a list of actions.
     def _sequence_actions(self, a1, as2):
-        from pyretic.core.language import drop, identity, Controller, CountBucket, DerivedPolicy
+        from pyretic.core.language import modify, drop, identity, Controller, CountBucket, DerivedPolicy
         while isinstance(a1, DerivedPolicy):
             a1 = a1.policy
         # TODO: be uniform about returning copied or modified objects.