<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _op(self, _, obj, app):
 """ convert status code in Responses from int to string """

        if obj.responses == None: return 

        tmp = {}
        for k, v in six.iteritems(obj.responses):
            if isinstance(k, six.integer_types):
                tmp[str(k)] = v
            else:
                tmp[k] = v
        obj.update_field('responses', tmp)