faulthandler part 2

Now, let's see how to dump stack trace when a specific signal is received. We will use SIGUSR1 but you can do the same for any signal.

import faulthandler
from signal import SIGUSR1
from time import sleep

faulthandler.register(SIGUSR1)
sleep(60)

Now, in a new terminal, find out the PID of the interpreter. If the file is named tmp.py, this is how you can do it (we add [] in grep to exclude the grep itself from the output):

ps -ax | grep '[t]mp.py'

The first number in the output is the PID. Now, use it to send the signal for PID 12345:

kill -SIGUSR1 12345

And back in the terminal with the running script. You will see the stack trace:

Current thread 0x00007f22edb29740 (most recent call first):
  File "tmp.py", line 6 in <module>

This trick can help you to see where your program has frozen without adding logs to every line. However, a better alternative can be something like py-spy which allows you to dump the current stack trace without any changes in the code.