def clean_dir(root):
    """remove .* and _* files and directories under root"""
    for x in root.walkdirs('.*', errors='ignore'):
        x.rmtree()
    for x in root.walkdirs('_*', errors='ignore'):
        x.rmtree()
    for x in root.walkfiles('.*', errors='ignore'):
        x.remove()
    for x in root.walkfiles('_*', errors='ignore'):
        x.remove()
