old_contents: from flask.ext.restplus import fields as basefields
  
  class Date(basefields.BaseField):
      __schema_type__ = 'date'
      __schema_format__ = None
  
      def schema(self):
          return {
              'type': self.__schema_type__,
              'format': self.__schema_format__,
              'title': self.title,
              'description': self.description,
              'readOnly': self.readonly,
          }
  
      def format(self):
          return self.isoformat()
  
      def output(self, key, value):
          return value[key].isoformat()
new_contents: from flask.ext.restplus import fields as basefields
  
  class Date(basefields.BaseField):
      __schema_type__ = 'date'
      __schema_format__ = None
  
      def schema(self):
          return {
              'type': self.__schema_type__,
              'format': self.__schema_format__,
              'title': self.title,
              'description': self.description,
              'readOnly': self.readonly,
          }
  
      def format(self):
          return self.isoformat()
  
      def output(self, key, value):
          if isinstance(value, dict):
              return value[key].isoformat()
          else:
              return getattr(value, key).isoformat()
subject: fix datetime fields