Fix json_format.py in py26

python/google/protobuf/json_format.py

@@ -271,8 +271,10 @@ def _ListValueMessageToJsonObject(message, unused_including_default=False):
 def _StructMessageToJsonObject(message, unused_including_default=False):
   """Converts Struct message according to Proto3 JSON Specification."""
   fields = message.fields
-  return {key: _ValueMessageToJsonObject(fields[key])
-          for key in fields}
+  ret = {}
+  for key in fields:
+    ret[key] = _ValueMessageToJsonObject(fields[key])
+  return ret
 
 
 def _IsWrapperMessage(message_descriptor):