PDB for n00bs
PDB is the python debugger, which is very handy for debugging scripts. I use it two ways.
If I’m having a problem with the script, I’ll put in the line
import pdb; pdb.set_trace()
just before where the problem occurs. Once the pdb line is hit, I get the interactive debugger and can start stepping through the program and seeing where it blows up, and what variables are getting set to before that happens.
However, I recently found a very handy second way. I was debugging a script with a curses interface, which cleans up when it exits. Unfortunately, that cleanup means that my terminal gets wiped when something crashes, so instead of a stack trace, I just get dumped back to the terminal when something goes wrong, with no information at all left on the screen.
Invoking the script with
python -m pdb ./my_script.py
gets me the postmortem debugger, so when something goes wrong, the program halts and I get the interactive debugger and some amount of stack trace. It’s messy looking because of curses, but I can at least see what is going on.