def url_path_join(*pieces):
    """Join components of url into a relative url
    Use to prevent double slash when joining subpath. This will leave the
    initial and final / in place
    """
    initial = pieces[0].startswith('/')
    final = pieces[-1].endswith('/')
    stripped = [s.strip('/') for s in pieces]
    result = '/'.join(s for s in stripped if s)
    if initial: result = '/' + result
    if final: result = result + '/'
    if result == '//': result = '/'
    return result