The following patch tries to improve how xmlrpc.client handles strings.
In particular, it simplifies the decoding of strings by keeping them as
unicode str.

Did you try these changes? Can you provide a test case?

I didn't test the changes extensively. I ran the test suite and the
changes seemed to be correct.

It is a bit difficult to provide a test case, since the patch shouldn't
change how the code currently behave. Nevertheless, here is a simple
example:

#!/usr/bin/python3.2
# xmlclient.py
import xmlrpc.client
server_proxy = xmlrpc.client.ServerProxy("http://localhost:8000")
print(server_proxy.print_str("être à montréal"))

#!/usr/bin/python2.6
# xmlserve.py
from SimpleXMLRPCServer import SimpleXMLRPCServer
def print_str(s):
  return (repr(type(s)), repr(s)) 
server = SimpleXMLRPCServer(("localhost", 8000))
server.register_function(print_str)
server.serve_forever()

And here's a sample run:

alex@helios:py3k$ python2.6 ./xmlserve.py > /dev/null &
alex@helios:py3k$ ./python ./xmlclient.py 
["<type 'str'>", "'Bonjour'"]
["<type 'unicode'>", "u'Je suis \\xe0 Montr\\xe9al'"]
[56836 refs]
alex@helios:py3k$ patch -p0 < simplify_xmlrpc_string_decoding.diff 
patching file Lib/xmlrpc/client.py
alex@helios:py3k$ ./python ./xmlclient.py 
["<type 'str'>", "'Bonjour'"]
["<type 'unicode'>", "u'Je suis \\xe0 Montr\\xe9al'"]
[56877 refs]

Oops, I forgot to update my client in my last message. The sample trace
run should make more sense now.

#!/usr/bin/python3.2
# xmlclient.py
import xmlrpc.client
server_proxy = xmlrpc.client.ServerProxy("http://localhost:8000")
print(server_proxy.print_str("Bonjour"))
print(server_proxy.print_str("Je suis à Montréal"))

Patch committed in r74156 (branches/py3k).