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.

Solution 1

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.

Solution 2

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!"

Comments

[2rs2ts]

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

[2rs2ts]

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

[anon582847382]

@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]

@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?

[VaFancy]

@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?

[anon582847382]

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

[VaFancy]

@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?

[anon582847382]

@VaFancy In that case, on a UNIX based system such as that, use the curses module. However I'm afraid that's where my help ends, as I am a Windows user I know next to nothing about curses so you'll have to do some digging or ask a separate question.

[VaFancy]

@AlexThornton You have already helped me a lot and I appreciate it. I will try to find out how to solve this. BTW, it seems that I spelled your name incorrectly all the time.