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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):
    '''
    Read the last btmp file and return information on the failed logins
    '''
    ret = []

    users = {}
    groups = {}
    defaults = None

    for config_item in config:
        if 'users' in config_item:
            users = config_item['users']

        if 'groups' in config_item:
            groups = config_item['groups']

        if 'defaults' in config_item:
            defaults = config_item['defaults']

    with salt.utils.files.fopen(BTMP, 'rb') as fp_:
        loc = __context__.get(LOC_KEY, 0)
        if loc == 0:
            fp_.seek(0, 2)
            __context__[LOC_KEY] = fp_.tell()
            return ret
        else:
            fp_.seek(loc)
        while True:
            now = datetime.datetime.now()
            raw = fp_.read(SIZE)
            if len(raw) != SIZE:
                return ret
            __context__[LOC_KEY] = fp_.tell()
            pack = struct.unpack(FMT, raw)
            event = {}
            for ind, field in enumerate(FIELDS):
                event[field] = pack[ind]
                if isinstance(event[field], salt.ext.six.string_types):
                    if isinstance(event[field], bytes):
                        event[field] = salt.utils.stringutils.to_unicode(event[field])
                    event[field] = event[field].strip('\x00')

            for group in groups:
                _gather_group_members(group, groups, users)

            if users:
                if event['user'] in users:
                    _user = users[event['user']]
                    if isinstance(_user, dict) and 'time_range' in _user:
                        if _check_time_range(_user['time_range'], now):
                            ret.append(event)
                    else:
                        if defaults and 'time_range' in defaults:
                            if _check_time_range(defaults['time_range'],
                                                 now):
                                ret.append(event)
                        else:
                            ret.append(event)
            else:
                if defaults and 'time_range' in defaults:
                    if _check_time_range(defaults['time_range'], now):
                        ret.append(event)
                else:
                    ret.append(event)
    return ret