paths: splitall(), relativepath()

[Martin Bless]

I was looking for a function that returns the relative path to a file
when looking from a specified directory. Here's what seems to do the
job. 

Somebody discovers any pitfalls?

I could imagine it would be nice to have splitall() and relativepath()
funcionality somewhere in the standard library.

Have a nice day,

mb - Martin Bless


import os
import sys

def splitall(path):
    """Split a path into all of its parts.
    
    From: Python Cookbook, Credit: Trent Mick
    """
    allparts = []
    while 1:
        parts = os.path.split(path)
        if parts[0] == path:
            allparts.insert(0, parts[0])
            break
        elif parts[1] == path:
            allparts.insert(0, parts[1])
            break
        else:
            path = parts[0]
            allparts.insert(0, parts[1])
    return allparts

def relativepath(fromdir, tofile):
    """Find relative path from 'fromdir' to 'tofile'.

    An absolute path is returned if 'fromdir' and 'tofile'
    are on different drives. Martin Bless, 2004-03-22.
    """
    f1name = os.path.abspath(tofile)
    if os.path.splitdrive(f1name)[0]:
        hasdrive = True
    else:
        hasdrive = False
    f1basename = os.path.basename(tofile)
    f1dirname = os.path.dirname(f1name)
    f2dirname = os.path.abspath(fromdir)
    f1parts = splitall(f1dirname)
    f2parts = splitall(f2dirname)
    if hasdrive and (f1parts[0].lower() <> f2parts[0].lower()):
        "Return absolute path since we are on different drives."
        return f1name
    while f1parts and f2parts:
        if hasdrive:
            if f1parts[0].lower() <> f2parts[0].lower():
                break
        else:
            if f1parts[0] <> f2parts[0]:
                break
        del f1parts[0]
        del f2parts[0]
    result = ['..' for part in f2parts]
    result.extend(f1parts)
    result.append(f1basename)
    return os.sep.join(result)
        
if 1 and __name__=="__main__":
    "demonstrate relativepath(...)"
    tofile = "C:/py/docutils/stylesheets/default.css"
    fromdir = "c:/PY/some/demo/currentdir"
    print "fromdir.....: ", fromdir
    print "tofile......: ", tofile
    print "relativepath: ", relativepath(fromdir,tofile)
    r"""Should print:
fromdir.....:  c:/PY/some/demo/currentdir
tofile......:  C:/py/docutils/stylesheets/default.css
relativepath:  ..\..\..\docutils\stylesheets\default.css
    """
    print "Done."