[Python-Dev] Proposed: add support for UNC paths to all functions in ntpath

[Michael Foord]

Larry Hastings wrote:
>
> I've written a patch for Python 3.1 that changes os.path so it handles 
> UNC paths on Windows:
>
>   http://bugs.python.org/issue5799

+1 for the feature. I have to deal with Windows networks from time to 
time and this would be useful.

Michael

>
> In a Windows path string, a UNC path functions *exactly* like a drive
> letter.  This patch means that the Python path split/join functions
> treats them as if they were.
>
> For instance:
>    >>> splitdrive("A:\\FOO\\BAR.TXT")
>    ("A:", "\\FOO\\BAR.TXT")
>
> With this patch applied:
>    >>> splitdrive("\\\\HOSTNAME\\SHARE\\FOO\\BAR.TXT")
>    ("\\\\HOSTNAME\\SHARE", "\\FOO\\BAR.TXT")
>
> This methodology only breaks down in one place: there is no "default
> directory" for a UNC share point.  E.g. you can say
>    >>> os.chdir("c:")
> or
>    >>> os.chdir("c:foo\\bar")
> but you can't say
>    >>> os.chdir("\\\\hostname\\share")
> But this is irrelevant to the patch.
>
> Here's what my patch changes:
> * Modify join, split, splitdrive, and ismount to add explicit support
>  for UNC paths.  (The other functions pick up support from these four.)
> * Simplify isabs and normpath, now that they don't need to be delicate
>  about UNC paths.
> * Modify existing unit tests and add new ones.
> * Document the changes to the API.
> * Deprecate splitunc, with a warning and a documentation remark.
>
> This patch adds one subtle change I hadn't expected.  If you call
> split() with a drive letter followed by a trailing slash, it returns the
> trailing slash as part of the "head" returned.  E.g.
>    >>> os.path.split("\\")
>    ("\\", "")
>    >>> os.path.split("A:\\")
>    ("A:\\", "")
> This is mentioned in the documentation, as follows:
>    Trailing slashes are stripped from head unless it is the root
>    (one or more slashes only).
>
> For some reason, when os.path.split was called with a UNC path with only
> a trailing slash, it stripped the trailing slash:
>    >>> os.path.split("\\\\hostname\\share\\")
>    ("\\\\hostname\\share", "")
> My patch changes this behavior; you would now see:
>    >>> os.path.split("\\\\hostname\\share\\")
>    ("\\\\hostname\\share\\", "")
> I think it's an improvement--this is more consistent.  Note that this
> does *not* break the documented requirement that
> os.path.join(os.path.split(path)) == path; that continues to work fine.
>
>
> In the interests of full disclosure: I submitted a patch providing this
> exact behavior just over ten years ago.  GvR accepted it into Python
> 1.5.2b2 (marked "*EXPERIMENTAL*") and removed it from 1.5.2c1.
>
> You can read GvR's commentary upon removing it; see comments in
> Misc/HISTORY <http://svn.python.org/view/python/trunk/Misc/HISTORY> 
> dated "Tue Apr  6 19:38:18 1999".  If memory serves
> correctly, the problems cited were only on Cygwin.  At the time Cygwin
> used "ntpath", and it supported "//a/foo" as an alias for "A:\\FOO". 
> You can see how this would cause Cygwin problems.
>
> In the intervening decade, two highly relevant things have happened:
> * Python no longer uses ntpath for os.path on Cygwin.  Instead it uses
>  posixpath.
> * Cygwin removed the "//a/foo" drive letter hack.  In fact, I believe it
>  now support UNC paths.
> Therefore this patch will have no effect on Cygwin users.
>
>
> What do you think?
>
>
> /larry/
>
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