python中 train_df = pd.read_excel(os.path.join(raw_data_dir,"train.xlsx")) answer_df = pd.read_excel(os.path.join(raw_data_dir,"answer.xlsx")) val_df = pd.read_excel(os.path.join(raw_data_dir,"val.xlsx"))这三行代码什么意思

这三行代码是在Python中使用pandas库读取Excel文件的数据。其中，train_df、answer_df和val_df是DataFrame类型的变量，分别对应train.xlsx、answer.xlsx和val.xlsx文件中的数据。os.path.join(raw_data_dir,"train.xlsx")、os.path.join(raw_data_dir,"answer.xlsx")和os.path.join(raw_data_dir,"val.xlsx")是用来将文件路径名连接起来的函数，其中raw_data_dir是存储原始数据的文件夹路径。