I make a directory on the way, but I don't want it to remain at the end. I put temporary data in the database, but I don't want it to remain at the end. Please let me know when the program is finished, whether it is normal or dead.
This is a way to achieve this.
This time, I will aim for the following things.
I will try several methods. For those who are in a hurry, I will write the conclusion first.
import sys
import time
import signal
def setup():
print("!!!Set up!!!")
def cleanup():
print("!!!Clean up!!!")
#Cleanup processing various
time.sleep(10)
print("!!!Clean up Done!!!")
def sig_handler(signum, frame) -> None:
sys.exit(1)
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
try:
#Various processing
time.sleep(60)
finally:
signal.signal(signal.SIGTERM, signal.SIG_IGN)
signal.signal(signal.SIGINT, signal.SIG_IGN)
cleanup()
signal.signal(signal.SIGTERM, signal.SIG_DFL)
signal.signal(signal.SIGINT, signal.SIG_DFL)
if __name__ == "__main__":
sys.exit(main())
Prepare the setup () / clean () function and the main part.
def setup():
print("!!!Set up!!!")
def cleanup():
print("!!!Clean up!!!")
def main():
pass
if __name__ == "__main__":
sys.exit(main())
The first thing that comes to mind is to use try --finally.
def main():
setup()
try:
print("Do some jobs")
finally:
cleanup()
Let's run it.
!!!set up!!!
do some jobs
!!!Clean up!!!
It has been cleaned up. But what if an error occurs along the way?
def main():
setup()
try:
print(1 / 0)
finally:
cleanup()
I will try it.
!!!set up!!!
!!!Clean up!!!
Traceback (most recent call last):
File "./try-finally.py", line 26, in <module>
sys.exit(main())
File "./try-finally.py", line 19, in main
print(1 / 0)
ZeroDivisionError: division by zero
This has also been cleaned up.
But what if you stop with Ctrl-C?
def main():
setup()
try:
time.sleep(60)
finally:
cleanup()
Run it and press Ctrl-C in the middle to stop it.
!!!Set up!!!
^C!!!Clean up!!!
Traceback (most recent call last):
File "./try-finally.py", line 27, in <module>
sys.exit(main())
File "./try-finally.py", line 20, in main
time.sleep(60)
KeyboardInterrupt
Apparently it worked.
But what if you kill it with kill?
!!!Set up!!!
Terminated
This should not be done. This will leave garbage files behind.
try --finally
Python has an atexit that runs it on exit. Let's try this.
def main():
setup()
atexit.register(cleanup)
print("Do some jobs")
Let's run it.
!!!Set up!!!
Do some jobs
!!!Clean up!!!
It went well. Next, let's get an error.
def main():
setup()
atexit.register(cleanup)
print(1 / 0)
I will try it.
!!!Set up!!!
Traceback (most recent call last):
File "./try-finally.py", line 25, in <module>
sys.exit(main())
File "./try-finally.py", line 21, in main
print(1 / 0)
ZeroDivisionError: division by zero
!!!Clean up!!!
This also worked. Compared to the case of try --finally, the clean up process is later.
So what if you stop with Ctrl-C?
def main():
setup()
atexit.register(cleanup)
time.sleep(60)
Run it and try to stop it with Ctrl-C in the middle.
!!!Set up!!!
^CTraceback (most recent call last):
File "./try-finally.py", line 25, in <module>
sys.exit(main())
File "./try-finally.py", line 21, in main
time.sleep(60)
KeyboardInterrupt
!!!Clean up!!!
feel well.
Then, finally, let's stop with kill.
!!!Set up!!!
Terminated
Sorry. Like try-finally, it doesn't seem to work either.
in atexit
The kill command sends a signal called SIGTERM to the process. Ctrl-C also sends a signal called SIGINT to the process. Let's try trapping these signals.
def sig_handler(signum, frame) -> None:
cleanup()
sys.exit(1)
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
signal.signal(signal.SIGINT, sig_handler)
print("Do some jobs")
I will try it.
!!!Set up!!!
Do some jobs
Clean up will not be performed. That's because the signal hasn't flown from the outside. It is natural. Since Exception is the same, confirmation is omitted.
Now let's see what happens with Ctrl-C.
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
signal.signal(signal.SIGINT, sig_handler)
time.sleep(60)
Run it and try to stop it with Ctrl-C in the middle.
!!!Set up!!!
^C!!!Clean up!!!
It's perfect. The KeyboardInterrupt Exception has disappeared, but it shouldn't usually be a problem. If absolutely necessary, you can raise (KeyboardInterrupt ()) in sig_handler.
Then, it is a kill to be worried about, but what will happen?
!!!Set up!!!
!!!Clean up!!!
Great! It was cleaned up with chitin.
So, try --finally or atexit and signal should be combined.
This time, assuming that the scope is narrow, I will try to combine try --finally and signal.
def sig_handler(signum, frame) -> None:
cleanup()
sys.exit(1)
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
try:
print("do some jobs")
finally:
signal.signal(signal.SIGTERM, signal.SIG_DFL)
cleanup()
It became like this. Ctrl-C also works with try --finally, so I tried to trap only SIGTERM. After exiting the try, cleanup should not be needed, so finally set SIGTERM back to the default.
Let's run it.
!!!Set up!!!
do some jobs
!!!Clean up!!!
As expected.
Next, let's get an error.
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
try:
print(1 / 0)
finally:
signal.signal(signal.SIGTERM, signal.SIG_DFL)
cleanup()
if __name__ == "__main__":
sys.exit(main())
I will try it.
!!!Set up!!!
!!!Clean up!!!
Traceback (most recent call last):
File "./try-finally.py", line 33, in <module>
sys.exit(main())
File "./try-finally.py", line 26, in main
print(1 / 0)
ZeroDivisionError: division by zero
It has been cleaned up.
Next, check Ctrl-C.
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
try:
time.sleep(60)
finally:
signal.signal(signal.SIGTERM, signal.SIG_DFL)
cleanup()
Run it and try pressing Ctrl-C in the middle.
!!!Set up!!!
^CClean up!!
Traceback (most recent call last):
File "./try-finally.py", line 33, in <module>
sys.exit(main())
File "./try-finally.py", line 26, in main
time.sleep(60)
KeyboardInterrupt
This has also been cleaned up.
Now, what about kill?
!!!Set up!!!
!!!Clean up!!!
!!!Clean up!!!
eh! It has been cleaned up twice.
By trapping SIGTERM, it seems that Python did not kill and executed finally. So, let's change sig_handler as follows.
def sig_handler(signum, frame) -> None:
sys.exit(1)
I stopped calling cleanup in the handler and just finished it.
Run it and try killing it.
!!!Set up!!!
!!!Clean up!!!
It's finally as expected.
The previous method is sufficient, but it is human nature to hit Ctrl-C repeatedly if you do not stop immediately after pressing Ctrl-C. You may also kill it many times.
I made the Cleanup process work, but that's a mess. So, I will not stop it during Cleanup.
def main():
setup()
signal.signal(signal.SIGTERM, sig_handler)
try:
time.sleep(60)
finally:
signal.signal(signal.SIGTERM, signal.SIG_IGN)
signal.signal(signal.SIGINT, signal.SIG_IGN)
cleanup()
signal.signal(signal.SIGTERM, signal.SIG_DFL)
signal.signal(signal.SIGINT, signal.SIG_DFL)
Ignore Ctrl-C and kill signals before cleanup (). After cleanup () is done, restore the default. This is perfect.
Looking at the results this time, it seems that the only difference between try-catch and atexit is the difference in scope and timing. If setup runs in the middle of a program, use try --finally at that scope. If setup is the first thing you run in your program, use atexit. If you want it to run anytime at the end, regardless of setup, use atexit. Does that mean?
Also, there is a way to use with, so if you are interested, please try it.
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