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I have some program logic that works as follows:

for i in range(10**6):
    foo(i)
    print("foo executed with parameter", i)
    bar(i)
    print("bar executed with parameter", i)

The problem arises when I want to interrupt the loop with Ctrl+C to raise a KeyboardInterrupt. I make sure that the function bar(i) always runs after the function foo(i); i.e. the loop cannot be interrupted between the two function calls (or, if it is, I want to complete the loop before exiting). If the interrupt is received while one of the functions is being executed, I want both to finish before exiting.

How is this achievable (with a try...except statement or otherwise) in Python 3?

Sergey
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  • `try` can't prevent interrupts from interrupting the code. The usual solution would be to replace the ctrl-C signal handler with one which merely sets a global value to `True`, and have the masked code examine this variable and terminate (perhaps by raising an exception) when it's set. – tripleee Jul 04 '22 at 10:33
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    here: https://stackoverflow.com/questions/1112343/how-do-i-capture-sigint-in-python , after it you can use the suggestion above to complete your puzzle – Omer Ben Haim Jul 04 '22 at 11:14

2 Answers2

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Thank you to Omer Ben Haim for providing an answer in the comments.

Indeed, the SIGINT signal can be captured using the signal module. Here is some proof-of-concept code that demonstrates this:

import signal
import time

stop = False

def handler(sig, frame):
    global stop
    stop = True

signal.signal(signal.SIGINT, handler)

############

i = 0
while i<10**6 and not stop:
    print("Part 1:", i)
    time.sleep(0.5)
    print("Part 2:", i)
    time.sleep(0.5)
    i += 1
Sergey
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-1

This could be done rather easily using a flag. When a KeyboardInterrupt is raised(E.g. Ctrl+c is pressed), you capture it and set the quit_loop flag to True.
When we finish what we need to do, we check if we need to quit the loop and if we do then we break.
If you want to fully exit the program you can replace break with exit().

quit_loop = False
for i in range(10):
    try:
        foo()
    except KeyboardInterrupt:
        quit_loop = True
    bar()

    if quit_loop:
        break
Tomer Hanochi
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