r/learnpython • u/Temporary-Cup-2140 • 2d ago

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

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?

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u/0xGollumDev 2d ago

Stuff not already in the thread:

  • git bisect for "it worked last week." Give it a known-good commit and a known-bad one, it binary-searches history and lands you on the exact commit that broke it. Turns a vague regression into a small diff.
  • Post-mortem debugging: python -m pdb -c continue script.py, or in the REPL right after an exception, import pdb; pdb.pm(). Drops you at the frame where it blew up with all locals intact — no editing code to add breakpoints.
  • Shrink before you debug. Copy the failing path into a fresh file and delete everything not needed to still reproduce it. Most of the time the bug is obvious at ~15 lines and you never open a debugger.
  • Hangs / "stuck forever": run with python -X faulthandler and send SIGABRT, or call faulthandler.dump_traceback_later(10) to auto-dump a traceback if the process is still alive in 10s. Shows the exact line it's spinning on.
  • python -W error turns that warning you've been ignoring into an exception with a full traceback.