On Sat, Apr 21, 2012 at 3:44 AM, Dan Stromberg <drsali...@gmail.com> wrote: > > On Thu, Apr 19, 2012 at 5:14 PM, Chris Angelico <ros...@gmail.com> wrote: >> >> The question then is whether to choose or auto-detect. Attempting to >> auto-detect could be quite inefficient; imagine if you have to call on >> ssh every couple of seconds, and something in $PATH is on a slow >> network share (or on a floppy drive, if you still have one of those). >> Yes, it's a poor choice of executable path, but it's perfectly legal, >> and the detection could get pathologically expensive. At very least, >> consider caching the result. > > The wrapper class for autodetecting could cache locations to speed things > up. bash does this normally (hence the "rehash" command), but probably not > across distinct shell processes.
Sure, but I wouldn't rely on your shell caching for you, which is why I suggested caching more locally. But it still means extra lookups. > I'm not a big fan of hardcoding paths; they have a way of changing. I > prefer $PATH, or $PATH search that caches. Nothing wrong with using $PATH, but when you have to search $PATH for not one but potentially three or more executables, it multiplies out your costs unnecessarily. >> Heh. Point. But the detection technique does depend on 'ssh' being the >> secure shell client and accepting parameters exactly like you're >> looking for - imagine if the Haiku (or whatever) ssh client takes >> slightly different params. How do you handle that with autodetection? > > True, that gets more complicated. > > For commands that look faintly similar but aren't really very similar, you'd > probably have a less-generic wrapper class that gets a usage message from > the ssh binary or something. The generic one is just for the simple case. This is sounding very much like a ./configure script and *not* something you want to do every startup. Suddenly you need a reliable detection method for your dependencies. I think it would be far simpler to record a table of commands, one per platform, and have the platform easily selectable. Which gets us right back to the aforementioned dictionary. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
