Python - KeyboardInterrupt or RuntimeError implementation

Question

New to python and programming. I have a program consist of several classes, module and functions. the program runs from a main class which calls several modules and function

My question is how to implement keyboardinterrupt if the user wants to terminate a running program at any point. Do I need to implement 'try/except' method in all the functions? or this can be implementable in the main function?

To catch interrupt at any moment do I need to use try/except in all the calling functions?

def KEYBOARD_INTERRUPT():
while True:
    yesnoinput=raw_input('Do you want to exit from software [Y/N]:') 
        if yesnoinput=='y' or yesnoinput.upper()=='Y':
            sys.exit()
        elif yesnoinput=='n' or yesnoinput.upper()=='N':
            break
        else:
            continue
def A():
    while True:
        try:
            userInput=raw_input("Please enter A")
            if userInput=='A':
                break
            else:
                continue
        except KeyboardInterrupt:
            KEYBOARD_INTERRUPT()

def B():

      userInput=raw_input("Please enter B")
      if userInput=='B':
            break
      else:
            continue

def main():
    try:
        A()
        B()
    except:
        KEYBOARD_INTERRUPT()

when main program is calling function B, at this moment if the user presses keyboardInterrupt the program will quit with error messgage, I am worried if I want to handle interrupt like KEYBOARD_INTERRUPT function I need to implement this in very function such as function A?

Did I understand wrong?

I think that depends on what you want to happen ... If you just want the user to have the ability to send a keyboard interrupt and have the program terminate, then you don't need to do anything (the exception will get raised and since you aren't catching it, it'll propagate and kill the program as all unhandled exceptions do) — mgilson
– mgilson, Commented Oct 11, 2016 at 3:25
but it will show error and terminate the program, need to catch the interrupt in proper way, say i have 20 different functions, do i need to implement this try/except in all these 20 functions? — mortuzahasan
– mortuzahasan, Commented Oct 11, 2016 at 3:30
Give it a try. For a console program, CTRL-C will exit your program with a default error message. If you want to do it differently, then catch it in your main program. — tdelaney
– tdelaney, Commented Oct 11, 2016 at 3:32
I think you need to define what "catch the interrupt in a proper way" actually entails... — mgilson
– mgilson, Commented Oct 11, 2016 at 3:32
when main program calls a function (for example, while loop waiting for user input), at that point the program enters to the calling function. would the interrupt in main function catch it? — mortuzahasan
– mortuzahasan, Commented Oct 11, 2016 at 3:34

tdelaney · Accepted Answer · 2016-10-11 03:45:40Z

Exceptions flow up the stack, terminating each function execution block as it goes. If all you want is a nice message, catch it at the top, in your main. This script has two mains - one that catches, one that doesnt. As you can see, the non-catcher shows a stack trace of where each function broke execution but its kinda ugly. The catcher masks all that - although it could still write the info to a log file if it wanted to.

import sys
import time

def do_all_the_things():
    thing1()

def thing1():
    thing2()

def thing2():
    time.sleep(120)

def main_without_handler():
    do_all_the_things()

def main_with_handler():
    try:
        do_all_the_things()
    except KeyboardInterrupt:
        sys.stderr.write("Program terminated by user\n")
        exit(2)

if __name__ == "__main__":
    # any param means catch the exception
    if len(sys.argv) == 1:
        main_without_handler()
    else:
        main_with_handler()

Run it from the console and hit ctrl-c and you get:

td@mintyfresh ~/tmp $ python3 test.py
^CTraceback (most recent call last):
  File "test.py", line 26, in <module>
    main_without_handler()
  File "test.py", line 14, in main_without_handler
    do_all_the_things()
  File "test.py", line 5, in do_all_the_things
    thing1()
  File "test.py", line 8, in thing1
    thing2()
  File "test.py", line 11, in thing2
    time.sleep(120)
KeyboardInterrupt
td@mintyfresh ~/tmp $ 
td@mintyfresh ~/tmp $ 
td@mintyfresh ~/tmp $ python3 test.py handled
^CProgram terminated by user

Claude · Accepted Answer · 2016-10-11 03:26:19Z

0

You could do something like :

try:
...
   except KeyboardInterrupt: 
       Do something

answered Oct 11, 2016 at 3:26

Claude

115 bronze badges

Collectives™ on Stack Overflow

Python - KeyboardInterrupt or RuntimeError implementation

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related