python - Exiting while loop by pressing enter without blocking. How can I improve this method?

Question

So I've been doing a little bit of reading up on how to exit a while loop by the user pressing the enter key and I've come up with the following:

import sys, select, os

switch = 1
i = 1
while switch == 1:
    os.system('cls' if os.name == 'nt' else 'clear')
    print "I'm doing stuff. Press Enter to stop me!"
    print i
    while sys.stdin in select.select([sys.stdin], [], [], 0)[0]:
        line = raw_input()
        if not line:
            print "Finished! =]"
            switch = 0
        else:
            print "Finished! =]"
            switch = 0
    i = i+1

Is there a way to tidy this up? In particular the "if not line" and the following "else" look messy. Can they be combined into one? A better alternative to using "switch"?

Initially if I typed a bunch of characters and then hit enter it didn't stop the loop. I would have to press enter again. The if not and else components are intended to set it up such that it would exit on the first press of enter.

Why not get rid of the if, as it does the same either way? Also, while True and break is neater than a flag — jonrsharpe
Does this actually work on Windows? The docs say that select.select only supports sockets on Windows: docs.python.org/2/library/select.html — Weeble
@Weeble I think this should work for Windows? code.activestate.com/recipes/… I'm coding on Ubuntu, personally. — user3394391

limasxgoesto0 limasxgoesto0 · Accepted Answer · 2014-03-13T21:31:16

This worked for me:

import sys, select, os

i = 0
while True:
    os.system('cls' if os.name == 'nt' else 'clear')
    print "I'm doing stuff. Press Enter to stop me!"
    print i
    if sys.stdin in select.select([sys.stdin], [], [], 0)[0]:
        line = raw_input()
        break
    i += 1

You only need to check for the stdin being input once (since the first input will terminate the loop). If the conditions line/not line have result for you, you can combine them to one if statement. Then, with only one while statement being used, you can now use break instead of setting a flag.

python - Exiting while loop by pressing enter without blocking. How can I improve this method?

1 Answers