把 :: 展开

expand 把缩写的 IPv6 展开成八组、每组四位：

def expand(addr):
    if "::" in addr:
        head, tail = addr.split("::")
        h = head.split(":") if head else []
        t = tail.split(":") if tail else []
        groups = h + ["0"] * (8 - len(h) - len(t)) + t
    else:
        groups = addr.split(":")
    return ":".join(g.zfill(4) for g in groups)

e = expand("2001:db8::1")
print(e + "/" + str(len(e.split(":"))))