Goodbye Print, Hello Debugger - Nina Zakharenko DjangoCon 2019

This talk was given on Tuesday September 24th 2019 at DjangoCon US in San Diego.

Still debugging your code by using print? Learn how to level up your ability to troubleshoot complex code situations by using the power of a fully-featured debugger in this talk aimed at all levels of programming ability.

Debuggers allow you to examine your program state, watch as the values of important variables change, and even modify the content of variables on the fly. Once I gave up using print to debug and troubleshoot, my productivity as a programmer increased, and yours can too!

I’ll showcase the variety of debugger tools available - from pdb, the simplest command line debugger that’s part of the standard library, to fancy graphical debuggers available in Python IDEs. Join me as we walk through real code together using debugger tools in a hands-on way to help us diagnose problems and bugs. The skills you’ll learn in this talk will allow you to quickly use these tools in your own code bases for fun, school, or work.

https://2019.djangocon.us/talks/goodbye-print-hello-debugger/

Transcript

1. nina.to/djangocon2019 --- NINA ZAKHARENKO --- GOODBYE PRINT, HELLO DEBUGGER --- @NNJA
2. LIVETWEET #DJANGOCON @NNJA nina.to/djangocon2019
3. whoami? @nnja nnja ✏ nina.to nina.to/djangocon2019
4. WHY USE DEBUGGERS? @nnja • nina.to/ djangocon2019
5. DEMO APPLICATION @nnja • nina.to/djangocon2019
6. CALL API & GET JSON def repos_with_most_stars(languages, min_stars, sort, order): query = create_query(languages, min_stars) parameters = {"q": query, "sort": sort, "order": order} response = session.get(github_api_url, params=parameters) if response.status_code != 200: raise GitHubApiException(response.status_code) response_json = response.json() items = response_json["items"]
7. PRINT @nnja • nina.to/djangocon2019
8. A DEBUGGER HELPS YOU EXAMINE THE STATE OF A RUNNING PROGRAM @nnja • nina.to/djangocon2019
9. DEBUGGING @nnja • nina.to/djangocon2019
10. WHAT YOU'LL LEARN TODAY ‣ why use debuggers? ‣ breakpoints, other debugger fundamentals ‣ my workflow ‣ tools: pdb, ipdb, IDEs ‣ breakpoint() in Python 3.7 ‣ demos, tips & tricks, when to use what @nnja • nina.to/djangocon2019
11. (THIS IS MY WAY) NOT ONE "RIGHT" WAY @nnja • nina.to/djangocon2019
12. TYPES OF DEBUGGERS @nnja • nina.to/djangocon2019
13. CLI ‣ pdb (in standard library) ‣ ‣ ipdb- ipdb (via pip install ipdb) ‣ & more... @nnja • nina.to/djangocon2019
14. @nnja
15. GRAPHICAL DEBUGGERS ‣ pudb (graphical CLI) ‣ IDEs ‣‣ Visual Studio Code ‣PyCharm ‣ & others ... @nnja • nina.to/djangocon2019
17. BREAKPOINTS @nnja • nina.to/djangocon2019
18. PYTHON 3.7? USE breakpoint() @nnja • nina.to/djangocon2019
19. breakpoint() ADVANTAGES ‣ set your debugger of choice (I like ipdb) ‣export PYTHONBREAKPOINT=ipdb.set_trace (only in Python >= 3.7) @nnja • nina.to/djangocon2019
20. breakpoint() ADVANTAGES environment variable that allows you skip all debug breakpoints $ PYTHONBREAKPOINT=0 python3.7 prod_code.py (only in Python >= 3.7) @nnja • nina.to/djangocon2019
21. CLI BREAKPOINTS IN PYTHON < 3.7 ‣ #1 Add them directly to your code import pdb; pdb.set_trace() # or import ipdb; ipdb.set_trace() ‣ #2: Set them interactively $ python -m pdb hello.py (Pdb) break 7 Breakpoint 1 at hello.py:7 @nnja • nina.to/djangocon2019
22. DEBUGGER FUNDAMENTALS @nnja • nina.to/djangocon2019
23. 5 MOST IMPORTANT COMMANDS ‣ l(ist) or ll for long list ‣ n(ext) - next line ‣ s(tep) - into ‣ c(ontinue) - until next breakpoint ‣ h(elp) <optional command> @nnja • nina.to/djangocon2019
24. @nnja • nina.to/djangocon2019
25. DEBUGGERS IN IDES @nnja • nina.to/djangocon2019
26. PYTHON EXTENSION FOR VS CODE ‣ 1. Download VS Code ‣ 2. Install Python Extension ‣ 3. Create a Debugger Configuration ‣
27. VISUAL BREAKPOINTS @nnja • nina.to/djangocon2019
28. WHEN TO USE WHAT? @nnja • nina.to/djangocon2019
29. WHEN TO USE WHAT? CLI DEBUGGING ‣ small programs and scripts ‣ want to work from command line IDE DEBUGGING ‣ complex code or large codebase ‣ debug templates @nnja • nina.to/djangocon2019
30. TIPS & TRICKS @nnja • nina.to/djangocon2019
31. TRICK: IPYTHON INTERACTIVE MODE ALIAS IN .PDBRC import IPython from traitlets.config import get_config cfg = get_config() # enable syntax highlighting cfg.InteractiveShellEmbed.colors = "Linux" cfg.InteractiveShellEmbed.confirm_exit = False alias interacti IPython.embed(config=cfg) download here: nina.to/pdbrc
32. ⚡ NEW! DEBUGGING JUPYTER NOTEBOOKS IN VS CODE nina.to/debug_jupyter @nnja • nina.to/djangocon2019
33. ! GOTCHAS @nnja • nina.to/djangocon2019
34. ! DON'T LEAVE BREAKPOINTS IN PRODUCTION CODE! @nnja • nina.to/djangocon2019
35. ! TIP: USE git pre-commit HOOKS ‣Prevent commits that match conditions ‣I use pre-commit.com ‣includes debug-statements hook ‣checks for: pdb, ipdb, pudb, breakpoint() & more @nnja
36. ! WRAPPING UP @nnja • nina.to/djangocon2019
37. FIXING BUGS IS A PROCESS OF CONFIRMING, ONE BY ONE, THAT THE THINGS YOU BELIEVE TO BE TRUE ABOUT THE CODE ARE TRUE. WHEN YOU FIND AN ASSUMPTION THAT ISN'T, YOU FOUND A CLUE. (Paraphrased from the art of debugging with GBS, DDD, and Eclipse) @nnja • nina.to/djangocon2019
38. ADDITIONAL RESOURCES ‣ Interactive pdb Tutorial (also in Korean) ‣ Python 3.7’s new builtin breakpoint — a quick tour THANKS ‣ ! Thea Flowers @nnja • nina.to/djangocon2019
39. THANKS! @NNJA SLIDES: nina.to/djangocon2019 PYTHON @ MICROSOFT: aka.ms/djangocon2019