'Return the name of the given device or None if we don\'t know.'

def get_device_name(self, device):

    if (device not in self.mac2name):
        url = 'http://{}/Status_Lan.live.asp'.format(self.host)
        data = self.get_ddwrt_data(url)
        if (not data):
            return None
        dhcp_leases = data.get('dhcp_leases', None)
        if (not dhcp_leases):
            return None
        cleaned_str = dhcp_leases.replace('"', '').replace("'", '').replace('    ', '')
        elements = cleaned_str.split(',')
        num_clients = int((len(elements) / 5))
        self.mac2name = {}
        for idx in range(0, num_clients):
            mac_index = ((idx * 5) + 2)
            if (mac_index < len(elements)):
                mac = elements[mac_index]
                self.mac2name[mac] = elements[(idx * 5)]
    return self.mac2name.get(device)
