python 生成 树状结构

forwarding_recp = re.compile(".*?发件人:(.*?);.*?发送时间:.*?收件人:(.*?)主题", re.S)

def parse_addr(addr, split_str=‘,‘):
    l = []
    if addr:
        for a in addr.split(split_str):
            l.append(utils.parseaddr(a)[1])
    return l

def gen_forwarding(con):  # 参数是解析过后的邮件正文
    re_ret = forwarding_recp.findall(con)
    forwarding = dict()
    for i in re_ret:
        from_addr = parse_addr(i[0])[0]
        to_addr = parse_addr(i[1], ";")
        del to_addr[-1]

        for k, v in forwarding.items():
            forwarding.clear()
            to_addr.remove(k)
            to_addr.append({k: v})
            forwarding[from_addr] = to_addr
        forwarding[from_addr] = to_addr
    return json.dumps(forwarding)