Terry J. Reedy <tjreedy@udel.edu> added the comment: I perhaps misunderstood your question. I ran files from the command line as as 'python whatever', not 'whatever' so only python would care about an extension. I do not have a file association to 'run' a file, with or without .py. I presume IDLE does same when one RUNs a file, except with pythonw. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue1626300> _______________________________________