Convert field_name to field_key.
               
        {"field_name": value} => {"field_key": value}

def convert_keys(self, pydict):
        """Convert field_name to field_key.
               
        {"field_name": value} => {"field_key": value}
        """
        new_dict = dict()
        for key, value in pydict.items():
            new_dict[self.get_field_key(key)] = value
        return new_dict