Определение мобильных операторов на python без использования регулярных выражений

def get_operator(phone):
    phone = str(phone)
    operator_code = phone[2:5]
    if operator_code in ['039', '067', '068', '096', '097', '098']: operator = 'kyivstar'
    elif operator_code in ['063', '073', '093']: operator = 'lifecell'
    elif operator_code in ['050', '066', '095', '099']: operator = 'vodafone'
    elif operator_code in ['091', '092', '094']: operator = 'ukrtelecom'
    else: operator = None
    return operator