Changing the index of a For loop in Python (outside if statement) [duplicate]

Question

I am trying to change the index of a for loop depending if a user wants to go to the previous image (index = index - 1) and if he wants to go the next image (index = index + 1) however, the index doesnt change in the outerloop (outside the if statements).

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

Thanks in advance.

you can't do this with for-loop. It will always get next value from range(). — furas
– furas, Commented Jan 21, 2020 at 13:05
This is it: you simply can't do that with a for loop - you need a while loop — ForceBru
– ForceBru, Commented Jan 21, 2020 at 13:06

dsvp9xyjsqmfvi8p · Accepted Answer · 2020-01-21 13:07:26Z

0

Not sure why the for loop is there, I'd be tempted to structure it more like so:

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

answered Jan 21, 2020 at 13:07

dsvp9xyjsqmfvi8p

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1 Comment

Beni billhardt Over a year ago

Thanks! The solution works. Yea, looking at it now, im not sure why I included a For loop.

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