So you have your Python program. And it’s hanging somewhere. You add print("I am here") around, but soon you get lost.

If only there was something like gdb and ctrl+c…

pdb enters the game

The Python debugger can help with this, but what if your script is somehow called by other scripts? Or maybe it’s a library you want to debug?

You can add this little snippet somewhere in your code:

def debug_signal_handler(signal, frame):
    import pdb
    pdb.set_trace()
import signal
signal.signal(signal.SIGUSR1, debug_signal_handler)

Then run your program, and

pkill -SIGUSR1 <your program name>

Or, better:

sudo ps -elf | grep <your program name>

And then

kill -SIGUSR1 <the PID from above>

You can surely script this up to be less ugly!

The iPython way

I usually find it hard to debug the data-structures. For sure there are better tools, but when you have an hammer, all problems are nails. So, add

from IPython import embed
embed()

where you want your program to stop. It will open an interactive shell, and from there you can run any command as they where written in your script.