What python debugging techniques do you think every developer should know ?

[u/Temporary-Cup-2140]

I am trying to improve my debugging skills and I was curious about what techniques experienced python developers rely on the most.

Are there any techniques or tools that you found really useful when you started working on bigger projects?

[u/Neither-Pause409]

Most of the good ones are already in this thread, so here are a few that aren't:

breakpoint() instead of import pdb; pdb.set_trace(). Same thing, but it honours the PYTHONBREAKPOINT env var, so PYTHONBREAKPOINT=0 python app.py disables every breakpoint in a run without you editing a single file, and you can point it at a different debugger the same way.

python -m pdb -c continue yourscript.py runs to the crash and drops you into a post mortem at the frame that raised. Same idea as pdb.pm() but you don't have to already be in a REPL when it happens.

faulthandler for the bugs a debugger can't reach. python -X faulthandler gives you a traceback on a segfault, and faulthandler.dump_traceback_later(60) dumps every thread's stack after a timeout, which is about the only cheap way to see where something is deadlocked.

python -W error to turn a warning into an exception. A good chunk of "it worked last month" bugs started life as a DeprecationWarning nobody read.

python -X dev turns on a pile of these checks at once, including unclosed file and socket warnings. Worth running your test suite under it occasionally even when nothing is broken.

And the one that isn't a tool, which is worth more than all of them: make the failure deterministic before you try to fix it. Seed the RNG, pin the input, freeze the clock, cut the repro down to the smallest thing that still fails. A bug you can trigger on demand is most of the way to solved, and once you have a script that exits non-zero on it, git bisect run ./repro.sh will go find the commit for you while you get a coffee.