[Python-bugs-list] [ python-Bugs-749261 ] os.path.split does not handle . & .. properly

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Bugs item #749261, was opened at 2003-06-04 20:03
Message generated for change (Comment added) made by jepler
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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=749261&group_id=5470

Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Curtis Siemens (csiemens)
Assigned to: Nobody/Anonymous (nobody)
Summary: os.path.split does not handle . & .. properly

Initial Comment:
The os.path.split() & posixpath.split() functions in my
opinion do not handle '.' & '..' at the end of a path
properly which causes os.path.dirname() &
os.path.basename() to also return the wrong result
because they are directly based on os.path.split().

I'll demonstrate the Unix Python case (the Windows
ntpath.py case is just a close parallel variation).

Example:
>python
Python 2.1.1
>>> posixpath.split('.')
('', '.')
>>> posixpath.split('..')
('', '..')

Yet:
>>> posixpath.split('./')
('..', '')
>>> posixpath.split('../')
('..', '')

Now '.' really represents './', and '..' really
represents '../'
Since the split() function simply uses a string split
on '/' to
find directories, it goofs up on this one case.  The
'.' and
'..' are like the slash character in the sense that
they all
only refer to directories.
The '.' & '..' can never be files in Unix or Windows, so I
think that the split() function should treat paths like:
    .
    ..
    dir/.
    dir/..
    /dir1/dir2/.
    /dir1/dir2/..
as not having a file portion, just as if:
    ./
    ../
    dir/./
    dir/../
    /dir1/dir2/./
    /dir1/dir2/../
respectively were given instead.

The fix in posixpath.py for this is just to put a
little path
processing code at the beginning of the split() function
that looks for the follow cases:
    if p in ['.','..'] or p[-2:] == '/.' or p[-3:] ==
'/..':
        p = p+'/'
And then go into all the regular split() code.
In fix in ntpath.py is very similar.

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Comment By: Jeff Epler (jepler)
Date: 2003-06-08 10:34

Message:
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user_id=2772

I don't believe this behavior is a bug.  os.path.split's task is to split the last component of a path from the other components, regardless of whether any of the components actually names a directory.

Another property of os.path.split is that eventually this loop will terminate:
    while path != "": path = os.path.split(path)[0]
with your proposed change, this would not be true for paths that initially contain a "." or ".." component (since os.path.split("..") -> ('..', ''))

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