you are strongly suggested to change the viewing default in file explorer to show extensions cgi instructions you can skip this until you are starting on cgi files opening cgi files in idle by convention the server programs that you will be writing end in cgithat is not an extension that is automatically associated with idle for editing if you want to open cgi file (or any other type but pyto edit (and never runfrom inside of idleit is possible to do this directly in many stepsbut it is easier to go indirectlystart py file you have in idle (like localcgiserver py)or if idleonwindows cmd is thereas in my www folderuse it to start idle to open cgi file from inside idleyou select open form the file menu like normallybut then notice the dropdown choice in the lower right of the file open window that probably shows python files py)change this file filter to all files *then all files in the current folder should be listednot grayed outand you can navigate to and choose the one you want saving new cgi file as with opening cgi fileset the format filter at the bottom of the dialog window to all files then enter the full file name with the cgi if you forget and do not change the file filtera pywill be added to your file name then you can rename it in file explorer running cgi scripts if you insist on doing cgi work in different foldercopy both startserver cmd and localcgiserver py as well as all related html and cgi files to that folderand then when you want to test your workstart the local server from there with startserver cmd at this point you can do all the web server based activities in there are number of stepsbe sure you carefully go through the list in the tutorial rememberhtml files calling cgi fileand cgi files used directly are only run in your web browser with url starting with localhost: /and only after you have local server running from the same folder otherwise nothing dynamic happens some special mac instructions while the python language changes slowlyoperating systems and setup methods change more rapidly with succeeding versions the attempt here is to keep all such information in one place for the mac os- operating system it may become out of date at any time will assume version of max osx of at least high sierra ( or laterupgrades are free appendices