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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 list_zones():
    '''
    Displays a list of available time zones. Use this list when setting a
    time zone using ``timezone.set_zone``

    :return: a list of time zones
    :rtype: list

    CLI Example:

    .. code-block:: bash

        salt '*' timezone.list_zones
    '''
    ret = salt.utils.mac_utils.execute_return_result(
        'systemsetup -listtimezones')
    zones = salt.utils.mac_utils.parse_return(ret)

    return [x.strip() for x in zones.splitlines()]