os.path.commonprefix inadequacies

[Rich Harkins]

Here's yet another way to do a common prefix, not sure about its performance
characteristics (assuming you have lists):

def commonprefix(*lists):
    assert len(lists) > 1
    l=zip(*lists)
    for n in xrange(len(l)):
        if filter(None,map(cmp,l[n][1:],l[n][0]*(len(l[n])-1))):
            return lists[0][:n]
    return lists[0]

# Some tests
print commonprefix(('a','b','c'),('a','b','x'),('a','b','c','y'))
# Returns ('a','b')
print commonprefix(('a','b'),('x'))
# Returns ()
print commonprefix(('x','y','z'),('x','y','z'))
# Returns ('x','y','z')

Hope this helps!
Rich