Returns the msisdn in E.164 international format.

def e_164(msisdn: str) -> str:
    """
    Returns the msisdn in E.164 international format.
    """
    # Phonenumbers library requires the + to identify the country, so we add it if it
    # does not already exist
    number = phonenumbers.parse("+{}".format(msisdn.lstrip("+")), None)
    return phonenumbers.format_number(number, phonenumbers.PhoneNumberFormat.E164)