Python小程序问题

一名python初学者，做习题写了下面的程序：检查新用户不能和老注册用户重名，包括大写。
就是不运行，也查不出问题，哪位给指点一下，谢谢。
current_users=("john","tom","parker","kitty","helen","Golden")
new_users=["alice","tom","peter","alex","kitty"]

current_users_lower=[]
for user_1 in current_users:
   current_users_lower.append(user_1.lower())

for new_user in new_users:
      if new_user.lower() in current_users_lower:
            print(new_user+" has already exist!")
      else:
            print(new_user+" is ok")

[此贴子已经被作者于2019-9-24 09:52编辑过]