Python:返回列表不起作用

Question

我正在尝试制作一个程序，可以在一个类(class)中添加/删除/显示学生，5 个类(class)是一个列表中的 5 个列表。

非常感谢您的帮助。

当我运行这段代码时:

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() 的末尾做了 return classes 但我发现这不起作用。我听从了一些建议，但实际上什么也没发生:/

Answer 1

您在 intro 方法中定义了 classes，即使它返回了它，您的 action1 方法也看不到任何任何地方名为 classes 的变量。

Relevant answer on Python scope和 relevant documentation .