friends = []def add_friend():    name = raw_input("please input friend name:")    friends.append(name)    foreach(friends)def del_friend():    name = raw_input("please input friend name who you want to delete:")    if friends.index(name)!=-1:        friends.remove(name)    foreach(friends)def update_friend():    name = raw_input("please input friend name who you want to update:")    index = friends.index(name)    name = raw_input("please input friend name new")    if index != -1:        friends[index] = name    foreach(friends)def query_friend():    name = raw_input("please input friend name to query:")    print(name)whencase={    1:lambda _:add_friend(),    2:lambda _:del_friend(),    3:lambda _:update_friend(),    4:lambda _:query_friend()}while True:    print("-"*40)    print("  1  :  添加用户名")    print("  2  :  删除用户名")    print("  3  :  修改用户名")    print("  4  :  查询用户名")    print("  5  :  退出系统")    print("-"*40)    #提示用户输入    numstr = raw_input("请输入功能序号")    if not numstr.isdigit():        break    numstr = int(numstr)    if numstr == 5:        break    elif numstr<5:        whencase[numstr]    else:        continue