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!') ...