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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 _get_serv(ret=None):
    '''
    Return a redis server object
    '''
    _options = _get_options(ret)
    global REDIS_POOL
    if REDIS_POOL:
        return REDIS_POOL
    elif _options.get('cluster_mode'):
        REDIS_POOL = StrictRedisCluster(startup_nodes=_options.get('startup_nodes'),
                                        skip_full_coverage_check=_options.get('skip_full_coverage_check'),
                                        decode_responses=True)
    else:
        REDIS_POOL = redis.StrictRedis(host=_options.get('host'),
                                       port=_options.get('port'),
                                       unix_socket_path=_options.get('unix_socket_path', None),
                                       db=_options.get('db'),
                                       decode_responses=True,
                                       password=_options.get('password'))
    return REDIS_POOL