Thanks for the report and patch.  You may find the following guidelines useful for your future contributions: http://www.python.org/dev/patches/

I have two questions about the proposed fix.  First, this line caught my eye:

  if tag.split(':')[1] == 'nil':

It seems wrong to handle a nil element from any namespace the same way.  I think namespaces should be supported properly or not at all.

Second point, can you point us to documentation about nil?  The Wikipedia article about XML-RPC and http://ontosys.com/xml-rpc/extensions.php agree that nil should not be a child of value, but say nothing about a namespace.  If it’s a band-aid for one specific server, I don’t think it’s acceptable.