把三个八进制数摊成 rwx

运行下面这段程序，填写它打印出来的结果。

def to_rwx(mode):
    s = ""
    for k in (0, 1, 2):
        d = (mode >> (3 * (2 - k))) & 7
        s = s + ("r" if d & 4 else "-")
        s = s + ("w" if d & 2 else "-")
        s = s + ("x" if d & 1 else "-")
    return s

print("/".join(to_rwx(m) for m in (0o644, 0o750, 0o600)))