os.path.join (folder, filename) ensures the path is correct for the system. On Windows, it uses backslashes (reports\summary.txt); on Linux and macOS it uses forward slashes (reports/summary.txt).

A CSV file is a “comma-separated values” file. In plain English, this is a text file that contains an unusually large amount of data. More often than not, this is used in order to create databases of ...