read_csv：

        filepath_or_buffer : str, pathlib.Path, py._path.local.LocalPath or any object with a read() method (such as a file handle or StringIO)

        The string could be a URL. Valid URL schemes include http, ftp, s3, and

        file. For file URLs, a host is expected. For instance, a local file could

        be file ://localhost/path/to/table.csv

to_csv：

        filepath_or_buffer : str or file handle,default None

        file path or object, if None is provided the result is returned as a string.

路径拼接可以直接使用‘+’号，而不用os.path.join

如to_csv（'/data/' + 'file'）