How to Kill a While Loop With a Keystroke

How to kill a while loop with a keystroke?

The easiest way is to just interrupt it with the usual Ctrl-C (SIGINT).

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

Since Ctrl-C causes KeyboardInterrupt to be raised, just catch it outside the loop and ignore it.

How to use Esc to stop a while loop?

Update your stop_loop method like this:

def stop_loop():
  global stop
  stop = 1
  return stop

If you don't declare global stop then instead of updating stop variable you defined at the beginning of the file you'll create a new local stop variable inside stop_loop method.

Probably read this for better understanding: https://realpython.com/python-scope-legb-rule/

How do I exit a while loop from a keypress without using KeyboardInterrupt? [python]

Here is the example I promised you.

I did not need to import any mods for this program, but I believe the msvcrt mod that I use to control keyboard input is Windows specific. Be that as it may; even though we use different methods to control keyboard input, I hope you will see how your stopwatch can be controlled by key presses while a main program repeatedly loops and handles keyboard input.

import time     # Contains the time.time() method.
import winsound # Handle sounds.
import msvcrt   # Has Terminal Window Input methods 
# ===========================================
# -------------------------------------------
# --              Kbfunc()                 --
# Returns ascii values for those keys that
# have values, or zero if not.
def kbfunc():
    return ord(msvcrt.getch()) if msvcrt.kbhit() else 0
# -------------------------------------------
# --           Get_Duration()              --
# Gets the time duration for the stopwatch.
def get_duration():
    value = input("\n How long do you want the timer to run? ")
    try:
        value = float(value)
    except:
        print("\n\t** Fatal Error: **\n Float or Integer Value Expected.\n")
        exit()
    return value
# ===========================================
#                   Body    
# ===========================================
# To keep the program as simple as possible, we will only use
# standard ascii characters. All special keys and non-printable
# keys will be ignored. The one exception will be the
# carriage return key, chr(13).
# Because we are not trapping special keys such as the
# function keys, many will produce output that looks like
# standard ascii characters. (The [F1] key, for example,
# shares a base character code with the simicolon.)

valid_keys = [] # Declare our valid key list.
for char in range(32,127):  # Create a list of acceptable characters that
    valid_keys.append(char) # the user can type on the keyboard.
valid_keys.append(13)       # Include the carriage return.

# ------------------------------------------
duration = 0
duration = get_duration()

print("="*60)
print(" Stopwatch will beep every",duration,"seconds.")
print(" Press [!] to turn Stopwatch OFF.")
print(" Press [,] to turn Stopwatch ON.")
print(" Press [@] to quit program.")
print("="*60)
print("\n Type Something:")
print("\n >> ",end="",flush = True)

run_cycle = True # Run the program until user says quit.
stopwatch = True # Turn the stopwatch ON.
T0 = time.time() # Get the time the stopwatch started running.

while run_cycle == True:
    # ------
    if stopwatch == True and time.time()-T0 > duration: # When the duration
        winsound.Beep(700,300)  # is over, sound the beep and then
        T0 = time.time()          # reset the timer.
    # -----
    key = kbfunc()
    if key == 0:continue # If no key was pressed, go back to start of loop.    
    
    if key in valid_keys: # If the user's key press is in our list..
        
        if key == ord(","): # A comma means to restart the timer.
            duration = get_duration()         # Comment line to use old duration.
            print(" >> ",end="",flush = True) # Comment line to use old duration.
            t0 = time.time()
            stopwatch = True
            continue # Remove if you want the ',' char to be printed.
        
        elif key == ord("!"): # An exclamation mark means to stop the timer.")
            stopwatch = False
            continue # Remove if you want the "!" to print.
        
        elif key == ord("@"):  # An At sign means to quit the program.
             print("\n\n Program Ended at User's Request.\n ",end="")
             run_cycle = False # This will cause our main loop to exit.
             continue # Loop back to beginning so that the at sign
                      # is not printed after user said to quit.
             
        elif key == 13: # The carriage return means to drop down to a new line.
            print("\n >> ",end="",flush = True)
            continue
             
        print(chr(key),end="",flush = True) # Print the (valid) character. 
        # Keys that are not in our list are simply ignored.

How to break this loop in Python by detecting key press

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.

Restart While Loop With Keypress

keyboard module has more features allowing different hooks/blockers.

Just use keyboard.wait(key) to block the control flow until key is pressed:

import keyboard
from time import sleep

key = "right shift"

while True:
    print("Running")
    sleep(0.5)
    if keyboard.is_pressed(key):
        print('waiting for `shift` press ...')
        keyboard.wait(key)

Sample interactive output:

Running
Running
Running
waiting for `shift` press ...
Running
Running
Running
Running
Running
waiting for `shift` press ...
Running
Running
Running
...

How to exit a while loop with a keystroke in C?

I think you mean the following as long as a spacebar followed by the enter key is acceptable given your comments above.

char input = 0;
while( input != ' ' )
{ 
  printf("Press space bar to continue...\n");
  scanf("%c",&input);
}

Or if you prefer, without hitting the enter key:

#include <stdio.h>

int main(int argc, char **argv)
{
  char input = 0;
  while( input != ' ' )
  { 
    printf("Press space bar to continue...\n");
    input = getch();
  }
}

This worked on my msysgit bash shell. BUT, some people will insist that it work on Linux as well. Which is fine I guess, I love Linux, but I said the above solution worked on msysgit. The following works on my, let me be specific, Oracle VM for Ubuntu 10.10.

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

int main(int argc, char **argv)
{
  char input = 0;
  while( input != ' ' )
  { 
    printf("Press space bar to continue...\n");
    input = mygetch();
  }
}

int mygetch(void)
{
  struct termios oldt, newt;
  int ch;
  tcgetattr( STDIN_FILENO, &oldt );
  newt = oldt;
  newt.c_lflag &= ~( ICANON | ECHO );
  tcsetattr( STDIN_FILENO, TCSANOW, &newt );
  ch = getchar();
  tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
  return ch;
}

The mygetch came from here.

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