def split_namespace(clark_name):
    """Return (namespace, localname) tuple for a property name in Clark Notation.

    Namespace defaults to ''.
    Example:
    '{DAV:}foo'  -> ('DAV:', 'foo')
    'bar'  -> ('', 'bar')
    """
    if clark_name.startswith("{") and "}" in clark_name:
        ns, localname = clark_name.split("}", 1)
        return (ns[1:], localname)
    return ("", clark_name)