Python报UnboundLocalError:变量sports_talk引用前未赋值如何解决？

这个UnboundLocalError报错的核心原因是Python的变量作用域规则：

• 如果你在函数内部对一个变量做赋值操作，Python默认会将这个变量识别为局部变量，不会再去读取外部的全局同名变量
• 你代码里的全局变量sports_talk，在函数what_question_hobby内部，只有choice == "Playing Sports"条件成立时才会被赋值，如果随机选中的爱好不是运动，第二个if sports_talk == True判断时就会读取未赋值的局部变量，直接触发报错。
• 额外注意：原代码还缺少random模块导入语句，修复完作用域问题后还会触发NameError，需要补上导入语句。

方案1：声明使用全局变量（快速修复） #

在函数开头加上global sports_talk声明，告诉Python这个变量用的是外部全局作用域的变量，修复后的完整代码如下：

import random
sports_talk = False
sports = ["Basketball", "Football", "Soccer"]
sports_response = ["What sports do you play?", "what sports do you play?"]
hobbies = ["Programming", "Playing Sports", "Art", "Singing", "Playing the Piano", "Watching YouTube"]
def what_question_hobby(questions):
    global sports_talk # 新增这行声明使用全局变量
    choice = random.choice(hobbies)
    if choice == "Playing Sports":
        sports_talk = True
        print(sports_talk)
        print("Bot: " + choice)
    if sports_talk == True:
        print("/hint ask him what sports he plays")
        info = input("You: ")
        if info in sports_response:
            print("Bot: " + random.choice(sports))
            sports_talk = False
while True:
    talking_input = input("You: ")
    if talking_input == "What do you enjoy?":
        what_question_hobby(talking_input)

方案2：避免使用全局变量（更规范的写法） #

全局变量容易引发不可预期的作用域问题，更推荐把状态作为参数传入函数，再把修改后的状态返回，修改示例：

import random
sports = ["Basketball", "Football", "Soccer"]
sports_response = ["What sports do you play?", "what sports do you play?"]
hobbies = ["Programming", "Playing Sports", "Art", "Singing", "Playing the Piano", "Watching YouTube"]
def what_question_hobby(questions, sports_talk):
    choice = random.choice(hobbies)
    if choice == "Playing Sports":
        sports_talk = True
        print(sports_talk)
        print("Bot: " + choice)
    if sports_talk == True:
        print("/hint ask him what sports he plays")
        info = input("You: ")
        if info in sports_response:
            print("Bot: " + random.choice(sports))
            sports_talk = False
    return sports_talk

if __name__ == "__main__":
    sports_talk = False
    while True:
        talking_input = input("You: ")
        if talking_input == "What do you enjoy?":
            sports_talk = what_question_hobby(talking_input, sports_talk)

内容的提问来源于stack exchange，提问作者Terrible Game Developer