Absolute to relative URL?

[Jeff Shannon]

In article <3CAC1665.8040209 at mxm.dk>, maxm at mxm.dk says...
> Thomas Guettler wrote:
> 
> 
> > Is there already a function in the standard python modules
> > which returns the a relative url given two absolute urls?
> > 
> > Example:
> > 
> > relative_url("http://foo/a/b/c", "http://foo/a/d")
> >  --> return: "../d"
> 
> I hope you mean that the result should be "../../d" ??

Actually, that's not quite correct (and neither are your code 
examples below, for the same reason).

In the URL 'http://foo/a/b/c', we could presume that 'foo' is a 
domain name, 'a' and 'b' are directories, and 'c' is a filename.  
Thus, the 'current directory' ('.') for this URL is //foo/a/b, 
and the parent directory ('..') is //foo/a.  Therefore, in this 
case, the O.P.'s initial relative URL ('../d') is correct.

The issue is complicated somewhat in that '//foo/a/b/c' can 
*also* be shorthand for '//foo/a/b/c/index.html' (or whatever the 
server's default-filename is).  If (and *only* if) the original 
URL is representing a default document, then your result would be 
the correct one.
 
There doesn't seem to be a way to determine whether a given URL 
represents a default document or not, however, without hitting 
the server in question to find out.  (I certainly wouldn't want 
to rely on the type of, or even existence of, a file extension 
for this purpose.  No rule says that HTML documents *must* use a 
.htm/.html extension...)

-- 

Jeff Shannon
Technician/Programmer
Credit International