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).

Sometimes we don't know exactly how many times we want to repeat an action or task. We might want to repeat it UNTIL something happens. When we are washing up, we don't wipe the sponge across the ...