题解 | #禁止重复注册#

current_users = ['Niuniu', 'Niumei', 'GURR', 'LOLO']
new_users = ['GurR', 'Niu Ke Le', 'LoLo', 'Tuo Rui Chi']
for i in new_users:
    for j in current_users:
        if i.lower() == j.lower():
            print(f'The user name {i} has already been registered! Please change it and try again!')
            break
    else:
        print(f'Congratulations, the user name {i} is available!')

for-else/while-else语句：在循环中没有执行break语句时便会执行else语句。