在 Python 中更改 For 循环的索引（在 if 语句之外）[重复]

Question

我正在尝试更改 for 循环的索引，具体取决于用户是否要转到上一个图像（索引 = 索引 - 1）以及他是否要转到下一个图像（索引 = 索引 + 1），但是，索引在外循环中没有变化（在 if 语句之外）。

flag = False
while flag == False:
    for i in range(len(all_image)):

        image = all_image[i]
        print(i)
        userchoice = easygui.buttonbox(msg, image = image, choices=choices)

        if userchoice == 'Next':
            i = i+1

        elif userchoice == 'Previous':
            i = i-1

        elif userchoice == 'cancel':
            print('test')
            flag = True
            break       

提前致谢。

Answer 1

不确定为什么会有 for 循环，我很想将它的结构更像这样：

flag = False
idx = 0 #idx is where we are in the image list, and it gets modified by use choices in the while loop.
while flag == False:
    image = all_image[idx]
    print(idx)
    userchoice = easygui.buttonbox(msg, image = image, choices=choices)

    if userchoice == 'Next':
        idx += 1
    elif userchoice == 'Previous':
        idx -= 1
    elif userchoice == 'cancel':
        print('test')
        flag = True
        break