new_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  import json
  from .utils import ClassRegistry
  
  serializers = ClassRegistry()
  
  
  @serializers.register('json')
  class JSONSerializer(object):
      "serialize to and from JSON"
      def load(self, serialized):
          return json.loads(serialized)
  
      def dump(self, obj):
          return json.dumps(obj)
  
subject: add JSON serializer