Debugging Python: Goodbye Print, Hello Debugger - Nina Zakharenko Live Coders Conf 2020

Still debugging your Python 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.

Transcript

1. nina.to/lcc2020 --- NINA ZAKHARENKO --- DEBUGGING PYTHON: GOODBYE PRINT, HELLO DEBUGGER --- @NNJA
2. LIVETWEET #LCCONF2020 @NNJA nina.to/lcc2020
3. whoami? @nnja nnja ✏ nina.to nina.to/lcc2020
4. WHY USE DEBUGGERS? @nnja
5. DEMO APPLICATION @nnja
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
8. A DEBUGGER HELPS YOU EXAMINE THE STATE OF A RUNNING PROGRAM @nnja
9. DEBUGGING @nnja
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
11. (THIS IS MY WAY) NOT ONE "RIGHT" WAY @nnja
12. TYPES OF DEBUGGERS @nnja
13. COMMAND LINE DEBUGGERS ‣ pdb (in standard library) ‣ ‣ ipdb- ipdb (via pip install ipdb) ‣ & more... @nnja
14. @nnja
15. GRAPHICAL DEBUGGERS ‣ pudb (graphical CLI) ‣ IDEs ‣‣ Visual Studio Code ‣PyCharm ‣ & others ... @nnja
17. BREAKPOINTS @nnja
18. PYTHON 3.7? USE breakpoint() @nnja
19. breakpoint() ADVANTAGES ‣ set your debugger of choice (I like ipdb) ‣export PYTHONBREAKPOINT=ipdb.set_trace (only in Python >= 3.7) @nnja
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
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
22. DEBUGGER FUNDAMENTALS @nnja
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
24. @nnja
25. DEBUGGERS IN CLIS IN ACTION @nnja
26. DEBUGGERS IN IDES @nnja
27. PYTHON EXTENSION FOR VS CODE ‣ 1. Download VS Code ‣ 2. Install Python Extension ‣ 3. Create a Debugger Configuration ‣
28. VISUAL BREAKPOINTS @nnja
29. DEMO @nnja
30. WHEN TO USE WHAT? @nnja
31. 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
32. TIPS & TRICKS @nnja
33. 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
34. ⚡ DEBUGGING JUPYTER NOTEBOOKS IN VS CODE Debug Jupyter @nnja
35. ! GOTCHAS @nnja
36. ! DON'T LEAVE BREAKPOINTS IN PRODUCTION CODE! @nnja
37. ! 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
38. ! WRAPPING UP @nnja
39. 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
40. ADDITIONAL RESOURCES ‣ Interactive pdb Tutorial (also in Korean) ‣ Python 3.7’s new builtin breakpoint — a quick tour THANKS ‣ ! Thea Flowers @nnja
41. THANKS! @NNJA SLIDES: nina.to/lcc2020 PYTHON @ MICROSOFT: aka.ms/lcc2020