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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 beacon(config):
    '''
    Emit the status of all devices returned by adb

    Specify the device states that should emit an event,
    there will be an event for each device with the
    event type and device specified.

    .. code-block:: yaml

        beacons:
          adb:
            - states:
                - offline
                - unauthorized
                - missing
            - no_devices_event: True
            - battery_low: 25

    '''

    log.trace('adb beacon starting')
    ret = []

    _config = {}
    list(map(_config.update, config))

    out = __salt__['cmd.run']('adb devices', runas=_config.get('user', None))

    lines = out.split('\n')[1:]
    last_state_devices = list(last_state.keys())
    found_devices = []

    for line in lines:
        try:
            device, state = line.split('\t')
            found_devices.append(device)
            if device not in last_state_devices or \
                    ('state' in last_state[device] and last_state[device]['state'] != state):
                if state in _config['states']:
                    ret.append({'device': device, 'state': state, 'tag': state})
                    last_state[device] = {'state': state}

            if 'battery_low' in _config:
                val = last_state.get(device, {})
                cmd = 'adb -s {0} shell cat /sys/class/power_supply/*/capacity'.format(device)
                battery_levels = __salt__['cmd.run'](cmd, runas=_config.get('user', None)).split('\n')

                for l in battery_levels:
                    battery_level = int(l)
                    if 0 < battery_level < 100:
                        if 'battery' not in val or battery_level != val['battery']:
                            if ('battery' not in val or val['battery'] > _config['battery_low']) and \
                                            battery_level <= _config['battery_low']:
                                ret.append({'device': device, 'battery_level': battery_level, 'tag': 'battery_low'})

                        if device not in last_state:
                            last_state[device] = {}

                        last_state[device].update({'battery': battery_level})

        except ValueError:
            continue

    # Find missing devices and remove them / send an event
    for device in last_state_devices:
        if device not in found_devices:
            if 'missing' in _config['states']:
                ret.append({'device': device, 'state': 'missing', 'tag': 'missing'})

            del last_state[device]

    # Maybe send an event if we don't have any devices
    if 'no_devices_event' in _config and _config['no_devices_event'] is True:
        if not found_devices and not last_state_extra['no_devices']:
            ret.append({'tag': 'no_devices'})

    # Did we have no devices listed this time around?

    last_state_extra['no_devices'] = not found_devices

    return ret