On Sun, Aug 1, 2010 at 13:37, Steven D'Aprano <st...@pearwood.info> wrote: > On Mon, 2 Aug 2010 04:29:39 am Richard D. Moores wrote: >> <http://tutoree7.pastebin.com/0AkVmRVJ> is a work in progress. If I >> could get the script to tell whether or not the pickle files already >> existed, I could radically revise it (yeah, functions and all :) ). >> So how to find if a file exists? > > The lazy way is with the os.file.exists() function: > > if os.file.exists(filename): > f = open(filename) > > > Of course, the lazy way usually ends up needing more work to fix the > bugs it introduces. This is 2010, you're running under a multi-process > operating system where a hundred other programs are sharing time with > you, possibly even a multi-user system with other people reading and > writing files. So the above is wrong, because there's no guarantee that > just because the file exists when you call os.file.exists it will still > be there a millisecond later when you call open. So the right way is to > ignore os.file.exists and just open the file, catching errors: > > try: > f = open(filename) > except IOError: > do_something_when_the_file_isnt_there() > else: > do_something_with_file(f)
OK, but there are actually 2 files that need to be checked. If either one or both are missing I need to create/recreate both. How do I do that your way? I've forgotten the little I knew about catching errors. My lazy way has it now as "if not (os.path.isfile(path1) and os.path.isfile(path2)):" Thanks, Dick _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
