Goodbye Print, Hello Debugger!

Still debugging your code with print statements? 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 print statements, 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/au19 --- NINA ZAKHARENKO --- GOODBYE PRINT, HELLO DEBUGGER --- @NNJA
2. whoami? @nnja nnja ✏ nina.to nina.to/au19
3. LIVETWEET #PYCONAU @NNJA nina.to/au19
4. 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/au19
5. (THIS IS MY WAY) NOT ONE "RIGHT" WAY @nnja • nina.to/au19
6. WHY USE DEBUGGERS? @nnja • nina.to/au19
7. DEMO APPLICATION @nnja • nina.to/au19
8. 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"]
9. PRINT @nnja • nina.to/au19
10. A DEBUGGER HELPS YOU EXAMINE THE STATE OF A RUNNING PROGRAM @nnja • nina.to/au19
11. DEBUGGING @nnja • nina.to/au19
12. FIXING BUGS IN CODE IS A PROCESS OF CONFIRMING, ONE BY ONE, THAT THE THINGS YOU BELIEVE TO BE TRUE ABOUT THE CODE ARE ACTUALLY 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/au19
13. TYPES OF DEBUGGERS @nnja • nina.to/au19
14. CLI ‣ pdb (in standard library) ‣ ‣ ipdb- ipdb (via pip install ipdb) ‣ & more... @nnja • nina.to/au19
15. @nnja
16. GRAPHICAL DEBUGGERS ‣ pudb (graphical CLI) ‣ IDEs ‣‣ Visual Studio Code ‣PyCharm ‣ & others ... @nnja • nina.to/au19
18. BREAKPOINTS @nnja • nina.to/au19
19. USE breakpoint() IN PYTHON 3.7 @nnja • nina.to/au19
20. breakpoint() ADVANTAGES ‣ set your debugger of choice (I like ipdb) ‣set: PYTHONBREAKPOINT=ipdb.set_trace @nnja • nina.to/au19
21. breakpoint() ADVANTAGES environment variable that allows you skip all debug breakpoints $ PYTHONBREAKPOINT=0 python3.7 prod_code.py @nnja • nina.to/au19
22. NOT PYTHON 3.7? OTHER WAYS TO SET BREAKPOINTS (CLI) ‣ #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/au19
23. DEBUGGER FUNDAMENTALS @nnja • nina.to/au19
24. 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/au19
26. DEBUGGERS IN CLIS IN ACTION @nnja • nina.to/au19
27. DEBUGGERS IN IDES @nnja • nina.to/au19
28. PYTHON EXTENSION FOR VS CODE ‣ 1. Download VS Code ‣ 2. Install Python Extension ‣ 3. Create a Debugger Configuration ‣
29. VISUAL BREAKPOINTS @nnja • nina.to/au19
30. DEMO @nnja • nina.to/au19
31. WHEN TO USE WHAT? @nnja • nina.to/au19
32. 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/au19
33. TIPS & TRICKS @nnja • nina.to/au19
34. 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
35. BONUS: DEBUGGING JUPYTER NOTEBOOKS IN VS CODE ! : aka.ms/pyblog @nnja • nina.to/au19
36. ! GOTCHAS @nnja • nina.to/au19
37. ! DON'T LEAVE BREAKPOINTS IN PRODUCTION CODE! @nnja • nina.to/au19
38. ! 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
39. ! WRAPPING UP @nnja • nina.to/au19
40. ADDITIONAL RESOURCES ‣ Interactive pdb Tutorial (also in Korean) ‣ Python 3.7’s new builtin breakpoint — a quick tour THANKS ‣ ! Thea Flowers @nnja • nina.to/au19
41. THANKS! @NNJA SLIDES: nina.to/au19 PYTHON @ MICROSOFT: aka.ms/au19py