How to stop a stopwatch with a keyboard press in python?

Question

I made a super rudimentary stopwatch in python, just to get myself more acclimated with it, (It's my first programming language)and I've been trying to get the code to stop running when a key is pressed (using keyboard interrupt) but the code basically ignores keyboard interrupt and keeps going on forever. (here's my code for reference)

# Time
import time
import sys
timeLoop = True
# Variables to keep track and display
Sec = 0
Min = 0
Hour = 0
# Begin Process
timeloop = True
while timeloop == True:
    try:
        Sec += 1
        print(str(Hour) + " Hrs " + str(Min) + " Mins " + str(Sec) + " Sec ")
        time.sleep(1)
        if Sec == 60:
            Sec = 0
            Min += 1
            print(str(Min) + " Minute")
            if Min == 60:       
                Sec = 0
                Min = 0 
                Hour += 1
                print(str(Hour) + " Hours")
    except KeyboardInterrupt:
        sys.exit(0)

Not necessarily answering the question, but why do you define `timeloop` twice, also you don't need to do `while timeloop == True:`, you can just do `while timeloop:` — Professor_Joykill, Jul 26 '17 at 17:40
In this case, since the timeloop variable is never used, it could just be `while True:`. — TWReever, Jul 26 '17 at 17:44

score 4 · Accepted Answer · answered Jul 26 '17 at 17:51

4

Use a second thread (https://en.wikipedia.org/wiki/Multithreading_(computer_architecture), How to use threading in Python?):

def quit_on_user_input():
    input = raw_input("Press any key to quit.")
    # thread will lock up and wait for user to input. That's why this is on a separate thread.
    sys.exit(0)

quit_thread = threading.Thread(target=quit_on_user_input, args=[])
quit_trhead.start()
# The rest of your code. quit_thread will run in the background and therefor won't lock up your main thread.

answered Jul 26 '17 at 17:51

Ian Kirkpatrick

1,861
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1

`raw_input()` requires the user to press enter. – Jim Wright Jul 26 '17 at 18:00
Thanks! Works well now :) – Deity3 Jul 26 '17 at 20:55
Great! Would you please mark this as the answer then? – Ian Kirkpatrick Jul 27 '17 at 13:16

Jim Wright · Answer 2 · 2017-07-26T18:08:16.263

The KeyboardInterrupt exception is thrown when the user quit's the program with ctrl + c. You will need to use another method to detect a key press. This answer seems to have a good cross-platform class to check stdin.

EDIT: The answer I linked above would require the user to press enter, so that could work if you run it in a different thread.

The following method should work on any keypress but only on Windows.

import msvcrt
# Time
import time
import sys
timeLoop = True
# Variables to keep track and display
Sec = 0
Min = 0
Hour = 0
# Begin Process
while True:
    try:
        Sec += 1
        print(str(Hour) + " Hrs " + str(Min) + " Mins " + str(Sec) + " Sec ")
        time.sleep(1)
        if Sec == 60:
            Sec = 0
            Min += 1
            print(str(Min) + " Minute")
            if Min == 60:
                Sec = 0
                Min = 0
                Hour += 1
                print(str(Hour) + " Hours")
        if msvcrt.kbhit():
            break
    except KeyboardInterrupt:
        break

EDIT2: Found a library for kbhit that has cross-platform support. In the example below I have saved it in the same directory as kbhit.py and have imported it at line #1.

from kbhit import KBHit
# Time
import time
import sys
timeLoop = True
# Variables to keep track and display
Sec = 0
Min = 0
Hour = 0

k = KBHit()
# Begin Process
while True:
    try:
        Sec += 1
        print(str(Hour) + " Hrs " + str(Min) + " Mins " + str(Sec) + " Sec ")
        time.sleep(1)
        if Sec == 60:
            Sec = 0
            Min += 1
            print(str(Min) + " Minute")
            if Min == 60:
                Sec = 0
                Min = 0
                Hour += 1
                print(str(Hour) + " Hours")
        if k.kbhit():
            break
    except KeyboardInterrupt:
        break

The problem with this is that the time it takes for the kbhit to be evaluated will throw off the timer. The timer MUST be a completely separate thread or else it will not truely be a millisecond. Devpending on how fast the processor is, we have no idea how long it could take to process kbhit. Especially with a slower language like Python. — Ian Kirkpatrick, Jul 26 '17 at 19:34

How to stop a stopwatch with a keyboard press in python?

2 Answers2