如何制作一个不和谐的机器人，如果他们的用户名是大写的，就给他们一个昵称(他们的用户名是小写的)

def generate_nickname(username):
    if username.isupper():
        return username.lower()
    else:
        return "No nickname"

# 测试代码
usernames = ["JOHN", "Alice", "MARY", "bob"]
for name in usernames:
    print(f"Username: {name}, Nickname: {generate_nickname(name)}")

Username: JOHN, Nickname: john
Username: Alice, Nickname: No nickname
Username: MARY, Nickname: mary
Username: bob, Nickname: No nickname