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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def update_hash(a_hash, mv):
 """Adds ``mv`` to ``a_hash`` Args: a_hash (`Hash`):
 the secure hash, e.g created by hashlib.md5 mv (:class:`MetricValue`):
 the instance to add to the hash """

    if mv.labels:
        signing.add_dict_to_hash(a_hash, encoding.MessageToPyValue(mv.labels))
    money_value = mv.get_assigned_value(u'moneyValue')
    if money_value is not None:
        a_hash.update(b'\x00')
        a_hash.update(money_value.currencyCode.encode('utf-8'))