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).

If a Windows upgrade has ever gone sideways on you, you know how vague and unhelpful the error messages can be. Here are my go-to troubleshooting tricks when that happens.

Peter Gratton, Ph.D., is a New Orleans-based editor and professor with over 20 years of experience in investing, risk management, and public policy. Peter began covering markets at Multex (Reuters) ...