python - Python:返回列表不起作用

我正在尝试制作一个可以在班级中添加/删除/显示学生的程序，这5个班级是列表中的5个列表。

非常感谢您的帮助。

当我运行此代码时：

global classes
def intro():
    print("Welcome to Powerschool v2.0!")
    print("Actions:")
    print("1. Add Student")
    print("2. Delete Student")
    print("3. Show Students in a Class")
    print("4. Show All Students")
    x = int(input())
    while x<1 or x>4:
        print ("Please choose an action, 1-4.")
        x = int(input())
    if x == 1:
        action1()
    elif x == 2:
        action2()
    elif x == 3:
        action3()
    elif x == 4:
        action4()
    classes = [[],[],[],[],[]]
    return classes
def action1():
    print("Which Class? 1-5")
    a = int(input())
    print("Please enter the student's name.")
    z = input()
    classes[a-1].append(z)
    again()
def action2():
    print ("Which Class? 1-5")
    print ("Which student?")
    again()
def action3():
    print ("Which Class? 1-5")
    y = int(input())
    if y == 1:
        print (classes[0])
    elif y == 2:
        print (classes[1])
    elif y == 3:
        print (classes[2])
    elif y == 4:
        print (classes[3])
    elif y == 5:
        print (classes[4])
    again()
def action4():
    print (classes)
    again()
def again():
    print("Would you like to do something else? y/n")
    h = input()
    if h == "y":
        intro()
    else:
        quit
def main():

    intro()

main()

我的错误是：

Traceback (most recent call last):
  File "C:\Documents and Settings\user1\My Documents\Downloads\az_studenttracker.py", line 67, in <module>
    main()
  File "C:\Documents and Settings\user1\My Documents\Downloads\az_studenttracker.py", line 65, in main
    intro()
  File "C:\Documents and Settings\user1\My Documents\Downloads\az_studenttracker.py", line 19, in intro
    action1()
  File "C:\Documents and Settings\user1\My Documents\Downloads\az_studenttracker.py", line 33, in action1
    classes[a-1].append(z)
NameError: name 'classes' is not defined

我在intro（）末尾做了return classes，但是我发现那是行不通的。
我遵循了一些建议，但没有真正发生任何事情：/

最佳答案

这是因为classes超出了后两种方法的范围。因此，您有两个选择：

选项1

将类传递给方法action1(), action2(), etc，如下所示：

def action1(classes)

...以及何时调用：

action1(classes) //with the classes var you just made

选项2（推荐）

只需将classes var放在您的方法外，或将其声明为global，如下所示：

global classes = [[],[],[],[],[]]

...就在之前：

def intro()

通常，您应该阅读有关退货的工作方式的信息。您编写的代码中没有必要

关于python - Python:返回列表不起作用，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/26950574/