def METHOD_NAME(cls, node, ns):
    """
    Generate a prefix.
    @param node: XML node on which the prefix will be used.
    @type node: L{sax.element.Element}
    @param ns: Namespace needing a unique prefix.
    @type ns: (prefix, URI)
    @return: I{ns} with a new prefix.
    @rtype: (prefix, URI)
    """
    for i in range(1, 1024):
        prefix = "ns%d" % (i,)
        uri = node.resolvePrefix(prefix, default=None)
        if uri in (None, ns[1]):
            return prefix, ns[1]
    raise Exception("auto prefix, exhausted")