Python函数内break无法终止外层while循环 无歌曲时如何直接结束程序

解决方案 #

你可以通过给fate函数增加返回状态的方式，向外层循环传递当前歌曲库存是否为空的信号，外层循环收到库存为空的信号后直接终止即可，修改后的代码如下：

import random
Genre = ["Power metal", "Melodic death metal", "Progressive metal", "Rock"]
Power_metal = ["Helloween", "Dragonforce", "Hammerfall"]
Melodic_death_metal = ["Kalmah", "Insomnium", "Ensiferum", "Wintersun"]
Progressive_metal = ["Dream theater", "Symphony X"]
Rock = ["Bon Jovi", "Nirvana"]

a = ["Pumpkins united", "Halloween"]

Helloween = set(a)

Music = input("\nSelect a music genre from available: %s:" % (Genre))
def bands(Music):
    while True:
        if Music == "Melodic death metal":
            return (Melodic_death_metal)
        elif Music == "Power metal":
            return (Power_metal)
        elif Music == "Progressive metal":
            return (Progressive_metal)
        elif Music == "Rock":
            return (Rock)
        else:
            Music = input("\nYou entered the wrong name. Please, enter again: %s:" % (Genre))

Band = input("\nReffering to chosen genre, I have bands such as: %s. Choose a specific band and I'll suggest a random song:\n" % bands(Music))
# 修改fate函数，增加返回值
def fate(Band):
    while True:
        if Band == "Helloween":
            if len(Helloween) != 0:
                print("Suggested song: ", Helloween.pop())
                return True # 还有剩余歌曲，返回True
            elif len(Helloween) == 0:
                print("I don't have more songs to propose. Enjoy your music")
                return False # 无剩余歌曲，返回False

# 首次调用获取初始库存状态
has_song = fate(Band)
# 仅当有剩余歌曲时才弹出继续询问
while has_song:
    next = input("\nWould you like me to suggest one more song from the band of your choice ?  Answer yes or no:\n")
    if next == "no":
        print("Enjoy your music")
        break
    elif next == "yes":
        has_song = fate(Band)
        # 无剩余歌曲时会自动终止循环，无需用户输入no

改动说明 #

• 调整fate函数逻辑，用return替代原有break语句，同时返回布尔值标记当前乐队是否还有未推荐的歌曲
• 新增has_song变量接收fate的返回值，将外层循环的触发条件修改为「还有剩余歌曲」，一旦fate返回库存为空的标记，外层循环会直接终止运行

内容的提问来源于stack exchange，提问作者Tomek