<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def retag(self, tagging, tag=None):
 """ Copies the object, applying a new tagging to it :param tagging: A dict containing the keys "explicit" and "implicit". Legacy API allows a unicode string of "implicit" or "explicit". :param tag: A integer tag number. Only used when tagging is a unicode string. :return: An Asn1Value object """


        # This is required to preserve the old API
        if not isinstance(tagging, dict):
            tagging = {tagging: tag}
        new_obj = self.__class__(explicit=tagging.get('explicit'), implicit=tagging.get('implicit'))
        new_obj._copy(self, copy.deepcopy)
        return new_obj