[Python-Dev] commonprefix - the beast just won't die... (original) (raw)

Skip Montanaro skip@mojam.com (Skip Montanaro)
Tue, 22 Aug 2000 09:45:27 -0500 (CDT)

I reverted the changes to {posix,nt,dos}path.commonprefix this morning, updated the tests (still to be checked in) and was starting to work on documentation changes, when I realized that something Guido said about using dirname to trim to the common directory prefix is probably not correct. Here's an example. The common prefix of ["/usr/local", "/usr/local/bin"] is "/usr/local". If you blindly apply dirname to that (which is what I think Guido suggested as the way to make commonprefix do what I wanted, you wind up with "/usr", which isn't going to be correct on most Unix flavors. Instead, you need to check that the prefix doesn't exist or isn't a directory before applying dirname. (And of course, that only works on the machine containing the paths in question. You should be able to import posixpath on a Mac and feed it Unix-style paths, which you won't be able to check for existence.)

Based on this problem, I'm against documenting using dirname to trim the commonprefix output to a directory prefix. I'm going to submit a patch with the test case and minimal documentation changes and leave it at that for now.

Skip