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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 add_expiration_postfix(expiration):
 """ Formats the expiration version and adds a version postfix if needed. :param expiration: the expiration version string. :return: the modified expiration string. """

    if re.match(r'^[1-9][0-9]*$', expiration):
        return expiration + ".0a1"

    if re.match(r'^[1-9][0-9]*\.0$', expiration):
        return expiration + "a1"

    return expiration