Obtain (uri, name) from a qualified name

def resolve_namespace(self, qname):
        """ Obtain (uri, name) from a qualified name """
        if ':' in qname:
            prefix, name = qname.split(':', 1)
            uri = self._ns[prefix]
        else:
            name = qname
            if None in self._ns:
                uri = self._ns[None]
            else:
                uri = None
        return (uri, name)