How to break this loop in Python by detecting key press

Question

from subprocess import call
try:
    while True:
        call (["raspivid -n -b 2666666.67 -t 5000 -o test.mp4"],shell=True)
        call (["raspivid -n -b 2666666.67 -t 5000 -o test1.mp4"],shell=True)
except KeyboardInterrupt:
    pass

I plan to make it breaking loop while I am pressing any button. However I tried lots of methods to break the and none of them worked.

There's no way that this is the only portion of the code. A KeyboardInterrupt would trip the except and the program would continue after that, but since that's the end of the shown program, it would terminate. — 2rs2ts
– 2rs2ts, Commented Mar 4, 2014 at 21:41
@2rs2ts Thank you for answering me. This is the latest version of my code. I saw it on someone's blog. Anyway, these methods can only break the loop while I am pressing control+c. What I am trying to do is breaking the loop by pressing any buttons. By the way, as you see, my code aims to record the video again and again until I press a button. Is that possible to stop recording immediately after pressing? — VaFancy
– VaFancy, Commented Mar 4, 2014 at 23:49
Reading any arbitrary key input is not as straightforward in Python. You could try this snippet I found when googling for "python detect key press." It's up to you to find a solution for that. — 2rs2ts
– 2rs2ts, Commented Mar 5, 2014 at 15:20

anon582847382 · Accepted Answer · 2014-03-04 21:41:34Z

8

You want your code to be more like this:

from subprocess import call

while True:
    try:
        call(["raspivid -n -b 2666666.67 -t 5000 -o test.mp4"], shell=True)
        call(["raspivid -n -b 2666666.67 -t 5000 -o test1.mp4"], shell=True)
    except KeyboardInterrupt:
        break  # The answer was in the question!

You break a loop exactly how you would expect.

edited Mar 4, 2014 at 21:41

answered Mar 4, 2014 at 21:30

anon582847382

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7 Comments

2rs2ts Over a year ago

The while loop is local to the scope of the try, so this will produce a syntax error.

anon582847382 Over a year ago

@2rs2ts Thank you very much, I failed to look at the way I would implement this and not just the keyword. Answer has been edited.

VaFancy Over a year ago

@AlexThomton Thank you for answering me. This is the latest version of my code. I saw it on someone's blog. Anyway, these methods can only break the loop while I am pressing control+c. What I am trying to do is breaking the loop by pressing any buttons. By the way, as you see, my code aims to record the video again and again until I press a button. Is that possible to stop recording immediately after pressing?

anon582847382 Over a year ago

@VaFancy you can get any keypress by putting if msvcrt.kbhit(): break in your while loop instead of a try-except structure.

VaFancy Over a year ago

@AlexThomton Many thanks. But as far as I know 'msvcrt' can only work on windows. I need the method that can working on Raspberry PI, is there any?

|

nvd · Accepted Answer · 2016-09-07 17:32:51Z

Use a different thread to listen for a "ch".

import sys
import thread
import tty
import termios
from time import sleep

breakNow = False

def getch():

    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)

    try:
        tty.setraw(sys.stdin.fileno())
        ch = sys.stdin.read(1)
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)

    return ch

def waitForKeyPress():

    global breakNow

    while True:
        ch = getch()

        if ch == "b": # Or skip this check and just break
            breakNow = True
            break

thread.start_new_thread(waitForKeyPress, ())

print "That moment when I will break away!"

while breakNow == False:
    sys.stdout.write("Do it now!\r\n")
    sleep(1)

print "Finally!"

Community · Accepted Answer · 2017-05-23 12:19:29Z

2

You could try this:

try:
    while True:
        do_something()
except KeyboardInterrupt:
    pass

Taken from: here

edited May 23, 2017 at 12:19

CommunityBot

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answered Mar 5, 2014 at 9:33

ederollora

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Comments

Adrian B · Accepted Answer · 2014-03-04 21:38:31Z

0

try this:

from subprocess import call
    while True:
        try:
            call (["raspivid -n -b 2666666.67 -t 5000 -o test.mp4"],shell=True)
            call (["raspivid -n -b 2666666.67 -t 5000 -o test1.mp4"],shell=True)
        except KeyboardInterrupt:
            break
        except:
            break

answered Mar 4, 2014 at 21:38

Adrian B

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2 Comments

2rs2ts Over a year ago

Why add the extra except? Silent failures! Arrrgh! Also the while is unnecessarily indented.

VaFancy Over a year ago

@AdrianB Thank you for answering me. It works as same as using one except. Are there any methods that can break a loop by pressing any keys?

Berni Gf · Accepted Answer · 2020-05-06 10:56:19Z

This is the solution I found with threads and standard libraries

Loop keeps going on until one key is pressed
Returns the key pressed as a single character string

Works in Python 2.7 and 3

import thread
import sys

def getch():
    import termios
    import sys, tty
    def _getch():
        fd = sys.stdin.fileno()
        old_settings = termios.tcgetattr(fd)
        try:
            tty.setraw(fd)
            ch = sys.stdin.read(1)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch
    return _getch()

def input_thread(char):
    char.append(getch())

def do_stuff():
    char = []
    thread.start_new_thread(input_thread, (char,))
    i = 0
    while not char :
        i += 1

    print "i = " + str(i) + " char : " + str(char[0])

do_stuff()

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