Breaking out of nested loops with user input

Question

Is there an efficient way to break out of a nested loop by having a user simply providing an input at the particular time they want to break out (e.g. press a key)? I have conditional statements in the loops themselves that I can use to break the loops, but if for example I simply want to stop the loops at any time yet still want the rest of the code to run, is there a simple way to do that? To clarify the motivation, I would like to do something like:

for x in xrange(1000):
    for y in xrange(1000):
        for z in xrange(1000):
            print x,y,z #function of loop
            if (user_has_pressed_key) == True: #a user input that 
                                               #can come at any time
                                               #but there should NOT be 
                                               #a prompt needed for each iteration to run
                break
        else:
            continue
        break
    else:
        continue
    break

I have considered using raw input, but would not want the loops to wait each iteration for the user as there will be numerous iterations. There appear to be some proposed solutions when using different packages, but even these seem to only be Windows-specific. I am running this code on multiple computers so would ideally want it to function on different OS.

You may want to take a look at the standard `signal` library for asynchronous events. — AChampion, Nov 09 '16 at 22:41

score 4 · Accepted Answer · edited Jan 29 '20 at 19:50

4

You can break out of the nested loops if the user issues a Ctrl+C keystroke, since it throws a KeyboardInterrupt exception:

try:
    for x in xrange(1000):
        for y in xrange(1000):
            for z in xrange(1000):
                print x,y,z #function of loop

except KeyboardInterrupt:
    print("Stopped nested loops")

edited Jan 29 '20 at 19:50

Josh Correia

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answered Nov 09 '16 at 23:40

Sebastian Wozny

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This is essentially what I was looking for. But out of curiosity, is there a way to implement a similar method without the try/except statement? – Mathews24 Nov 11 '16 at 15:53

score 0 · Answer 2 · edited Nov 10 '16 at 02:11

0

If you want the loop to break whenever any key is pressed by the user, then you can try this import:

from msvcrt import getch
while True:
    key = getch()
    if (key is not None): 
        break

edited Nov 10 '16 at 02:11

Addison

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answered Nov 10 '16 at 00:17

M. Abdulai

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Breaking out of nested loops with user input

2 Answers2