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).

Using Python's os.walk function to walk through a tree of files and directories. I'm a web guy; I put together my first site in early 1993. And so, when I started to do Python training, I assumed that ...