How to test if two strings point to the same file or directory?
Comparing file system paths as strings is very brittle. Is there a better way to test if two paths point to the same file or directory (and that will work across platforms?) Thanks, -Sandra -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
> Comparing file system paths as strings is very brittle. Is there a > better way to test if two paths point to the same file or directory > (and that will work across platforms?) os.path.samefile(filename1, filename2) os.path.sameopenfile(fileobject1, fileobject2) -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
On Sat, 16 Dec 2006 17:02:04 -0800, Sandra-24 wrote: > Comparing file system paths as strings is very brittle. Why do you say that? Are you thinking of something like this? /home//user/somedirectory/../file /home/user/file Both point to the same file. > Is there a > better way to test if two paths point to the same file or directory > (and that will work across platforms?) How complicated do you want to get? If you are thinking about aliases, hard links, shortcuts, SMB shares and other complications, I'd be surprised if there is a simple way. But for the simple case above: >>> import os >>> path = '/home//user/somedirectory/../file' >>> os.path.normpath(path) '/home/user/file' -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
Tim Chase wrote: > > Comparing file system paths as strings is very brittle. Is there a > > better way to test if two paths point to the same file or directory > > (and that will work across platforms?) > > os.path.samefile(filename1, filename2) > os.path.sameopenfile(fileobject1, fileobject2) > Nice try, but they don't "work across platforms". -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
>> Comparing file system paths as strings is very brittle. > > Why do you say that? Are you thinking of something like this? > > /home//user/somedirectory/../file > /home/user/file Or even ~/file > How complicated do you want to get? If you are thinking about aliases, > hard links, shortcuts, SMB shares and other complications, I'd be > surprised if there is a simple way. > > But for the simple case above: > import os path = '/home//user/somedirectory/../file' os.path.normpath(path) > '/home/user/file' I'd suggest os.path.samefile which should handle case-sensitive (non-win32) vs case-insensitive (win32) filenames, soft-links, and hard-links. Not sure it's prescient enough to know if you have two remote shares, it will unwind them to their full server-path name. Works here on my various boxes (Linux, MacOS-X and OpenBSD) here. I'd assume it's the same functionality on Win32. -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
On Sun, 17 Dec 2006 12:30:15 +1100, Steven D'Aprano wrote: >> Is there a >> better way to test if two paths point to the same file or directory >> (and that will work across platforms?) > > How complicated do you want to get? If you are thinking about aliases, > hard links, shortcuts, SMB shares and other complications, I'd be > surprised if there is a simple way. Almost, but not quite, platform independent. os.path.samefile(path1, path2) >From the docs: samefile(path1, path2) Return True if both pathname arguments refer to the same file or directory (as indicated by device number and i-node number). Raise an exception if a os.stat() call on either pathname fails. Availability: Macintosh, Unix http://docs.python.org/lib/module-os.path.html -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
>>> Comparing file system paths as strings is very brittle. Is there a >>> better way to test if two paths point to the same file or directory >>> (and that will work across platforms?) >> os.path.samefile(filename1, filename2) >> os.path.sameopenfile(fileobject1, fileobject2) > > Nice try, but they don't "work across platforms". Okay...double-checking the docs.python.org writeup, it apparently does "work across platforms" (Mac & Unix), just not "across *all* platforms", with Win32 being the obvious outlier. It seems a strange omission from Win32 python, even if it were filled in with only a stub...something like def samefile(f1, f2): return abspath(f1.lower()) == abspath(f2.lower()) it might not so gracefully handle UNC-named files, or SUBST'ed file-paths, but at least it provides an attempt at providing the functionality on win32. As it currently stands, it would be entirely too easy for a [Mac|*nix] programmer to see that there's a samefile() function available, use it successfully based on its docstring, only to have it throw an exception or silently fail when run on win32. -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
Tim Chase wrote: [snip] > I'd suggest os.path.samefile which should handle case-sensitive > (non-win32) vs case-insensitive (win32) filenames, soft-links, > and hard-links. Not sure it's prescient enough to know if you > have two remote shares, it will unwind them to their full > server-path name. Works here on my various boxes (Linux, MacOS-X > and OpenBSD) here. I'd assume it's the same functionality on Win32. > Assume nothing. Read the manual. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
On Dec 16, 8:30 pm, Steven D'Aprano <[EMAIL PROTECTED]> wrote: > On Sat, 16 Dec 2006 17:02:04 -0800, Sandra-24 wrote: > > Comparing file system paths as strings is very brittle.Why do you say that? > > Are you thinking of something like this? > > /home//user/somedirectory/../file > /home/user/file > > Both point to the same file. > > > Is there a > > better way to test if two paths point to the same file or directory > > (and that will work across platforms?)How complicated do you want to get? > > If you are thinking about aliases, > hard links, shortcuts, SMB shares and other complications, I'd be > surprised if there is a simple way. So would I. Maybe it would make a good addition to the os.path library? os.path.isalias(path1, path2) > But for the simple case above: > > >>> import os > >>> path = '/home//user/somedirectory/../file' > >>> os.path.normpath(path)'/home/user/file' The simplest I can think of that works for me is: def isalias(path1, path2): ... return os.path.normcase(os.path.normpath(path1)) == os.path.normcase(os.path.normpath(path2)) But that won't work with more complicated examples. A common one that bites me on windows is shortening of path segments to 6 characters and a ~1. -Dan -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
Tim Chase wrote: > >>> Comparing file system paths as strings is very brittle. Is there a > >>> better way to test if two paths point to the same file or directory > >>> (and that will work across platforms?) > >>os.path.samefile(filename1, filename2) > >>os.path.sameopenfile(fileobject1, fileobject2) > > > > Nice try, but they don't "work across platforms". > > Okay...double-checking the docs.python.org writeup, it apparently > does "work across platforms" (Mac & Unix), just not "across *all* > platforms", with Win32 being the obvious outlier. My bet would be that it really works on Unix only (OS/X qualifying as Unix) and not on older Mac setups. > It seems a > strange omission from Win32 python, even if it were filled in > with only a stub...something like > > def samefile(f1, f2): > return abspath(f1.lower()) == abspath(f2.lower()) > > it might not so gracefully handle UNC-named files, or SUBST'ed > file-paths, but at least it provides an attempt at providing the > functionality on win32. As it currently stands, it would be > entirely too easy for a [Mac|*nix] programmer to see that there's > a samefile() function available, use it successfully based on its > docstring, only to have it throw an exception or silently fail > when run on win32. The current setup will not "silently fail when run on win32". How could it? It doesn't exist; it can't be run. Python 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit (Intel)] on win 32 Type "help", "copyright", "credits" or "license" for more information. | >>> import os | >>> os.path.samefile Traceback (most recent call last): File "", line 1, in AttributeError: 'module' object has no attribute 'samefile' The only way it could "silently fail when run on win32" would be to have a "stub" which gave the wrong answer. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
Tim Chase wrote:
>>> Comparing file system paths as strings is very brittle.
>>
>> Why do you say that? Are you thinking of something like this?
>>
>> /home//user/somedirectory/../file
>> /home/user/file
>
> Or even
>
> ~/file
~ is interpreted as "my home directory" by the shell, but when it's used
in a path, it has no special meaning. open('~/foo.txt') tries to open a
file called foo.txt in a subdirectory of the current directory called '~'.
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Re: How to test if two strings point to the same file or directory?
Leif K-Brooks wrote:
> ~ is interpreted as "my home directory" by the shell, but when it's used
> in a path, it has no special meaning. open('~/foo.txt') tries to open a
> file called foo.txt in a subdirectory of the current directory called '~'.
That's what os.path.expanduser is for.
--
Erik Max Francis && [EMAIL PROTECTED] && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
It is much safer to obey than to rule.
-- Thomas a Kempis
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Re: How to test if two strings point to the same file or directory?
Sandra-24 wrote: > Comparing file system paths as strings is very brittle. Is there a > better way to test if two paths point to the same file or directory > (and that will work across platforms?) No. There are ways to do it for many operating systems, but there is no system-independent way. It's often not possible for files accessed across a network; the information just isn't being sent. John Nagle -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
Sandra-24 wrote: > Comparing file system paths as strings is very brittle. Is there a > better way to test if two paths point to the same file or directory > (and that will work across platforms?) I suspect that the "and that will work across platforms" parenthesis is in effect a killer. However, if you're prepared to waive that particular requirement, I can suggest reading this page for a Win32 possibility: http://timgolden.me.uk/python/win32_how_do_i/see_if_two_files_are_the_same_file.html TJG -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
> The current setup will not "silently fail when run on win32". How could > it? It doesn't exist; it can't be run. Ah...didn't know which it did (or didn't do) as I don't have a win32 box at hand on which to test it. In chasing the matter further, the OP mentioned that their particular problem was related to tilde-expansion/compression which python doesn't seem to distinguish. To take this into consideration, there's some advice at http://groups.google.com/group/comp.lang.python/browse_thread/thread/ee559c99d54d970b/b71cb7ac1b7be105 where Chris Tismer has an example function/module that uses Win32 API calls to normalize a path/filename to the short-name equiv. It looks like this could be integrated into the previous code I posted, so you'd have something like os.path.samefile = lambda f1, f2: ( LongToShort(abspath(f1)).lower() == LongToShort(abspath(f2)).lower() ) As stated, it's a bit fly-by-the-seat-of-the-pants as I don't have any boxes running Win32 here at home, but that would be the general gist of the idea. It would be handy to add it, as the semantic meaning is the same across platforms, even if the implementation details are vastly different. One of the reasons I use python is because it usually crosses platform boundaries with nary a blink. Just a few more ideas, -tkc -- http://mail.python.org/mailman/listinfo/python-list
Re: How to test if two strings point to the same file or directory?
It looks like you can get a fairly good apporximation for samefile on win32. Currently I'm using the algorithm suggested by Tim Chase as it is "good enough" for my needs. But if one wanted to add samefile to the ntpath module, here's the algorithm I would suggest: If the passed files do not exist, apply abspath and normcase to both and return the result of comparing them for equality as strings. If both paths pass isfile(), try the mecahnism linked to in this thread which opens both files at the same time and compares volume and index information. Return this result. If that raises an error (maybe they will not allow us to open them) Try comparing them using the approach suggested by Tim Chase, but if that works there should be some indication given that the comparison may not be accurate (raise a warning?). If that also fails, raise an error. This should allow samfile to be used on win32 in well over 99.9% of cases with no surprises. For the rest it will either return a result that is likely correct with a warning of some kind, or it will fail entirely. It's not perfect, but you can't acheive perfection here. It would, however, have far less surprises than newbies using == to compare paths for equality. And it would also make os.path.samefile available on another platform. os.path.sameopenfile could be implemented perfectly using the comparison of volume and index information alone (assuming you can get a win32 handle out of the open file object, which I think you can) If someone would be willing to write a patch for the ntpath tests I would be willing to implement samefile as described above or as agreed upon in further discussion. Then we can submit it for inclusion in the stdlib. -- http://mail.python.org/mailman/listinfo/python-list
