I have module I use for situations like this - where a process will be running for a long time but gets stuck sometimes for unknown and irreproducible reasons. Its a bit hacky, and only works on unix (requires signals):

import code, traceback, signal def debug(sig, frame): """Interrupt running process, and provide a python prompt for interactive debugging.""" d={'_frame':frame} # Allow access to frame object. d.update(frame.f_globals) # Unless shadowed by global d.update(frame.f_locals) i = code.InteractiveConsole(d) message = "Signal received : entering python shell.

Traceback:

" message += ''.join(traceback.format_stack(frame)) i.interact(message) def listen(): signal.signal(signal.SIGUSR1, debug) # Register handler

To use, just call the listen() function at some point when your program starts up (You could even stick it in site.py to have all python programs use it), and let it run. At any point, send the process a SIGUSR1 signal, using kill, or in python:

os.kill(pid, signal.SIGUSR1)

This will cause the program to break to a python console at the point it is currently at, showing you the stack trace, and letting you manipulate the variables. Use control-d (EOF) to continue running (though note that you will probably interrupt any I/O etc at the point you signal, so it isn't fully non-intrusive.

I've another script that does the same thing, except it communicates with the running process through a pipe (to allow for debugging backgrounded processes etc). Its a bit large to post here, but I've added it as a python cookbook recipe.