CUDA_VISIBLE_DEVICES 默认值必须为str, 否则split会报错

add a  file separator, it mainly  to avoid  missing the file path separator in yml

add a necessary check for checkpoints, if you miss the file prefix and it will not execute the checkpoints codes

remove the  useless parameters  and  update import

the function sample_iter_reader  is executed repatedly,so the common modules do not need to be executed repeatedly