How to check which line of a Python script is being executed?

Question

I've got a Python script which is running on a Linux server for hours, crunching some numbers for me. I'd like to check its progress, so I'd like to see what line is being executed right now. If that was a C or C++ program then I would just attach to the process with gdb -p <pid> and examine the stacktrace with where. Of course, I can do the same with the Python interpreter process, but I can't see the Python script's line in the stacktrace.

So, how can I find out which line of the Python script is being executed currently?

Answer 1

You can add a signal handler to the Python script that sends this information to the terminal, or to a file, then hit ^C in the terminal to send the signal to the process.

import signal

def print_linenum(signum, frame):
    print "Currently at line", frame.f_lineno

signal.signal(signal.SIGINT, print_linenum)

You could also use some other signal and use the kill command to send the signal, if you need ^C to be able to interrupt the script, or set a signal.alarm() to print the information periodically, e.g. once a second.

You could print out other things from the stack frame if you like; there's a lot there. See the attributes of frame objects in this table.