'Return a Zone instance.
:param zone_id: ID of the required zone
:type  zone_id: ``str``
:rtype: :class:`Zone`'

def get_zone(self, zone_id):

    zone = None
    zones = self.list_zones()
    for z in zones:
        if (z.id == zone_id):
            zone = z
    if (zone is None):
        raise ZoneDoesNotExistError(zone_id=zone_id, driver=self, value='')
    return zone
