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Debugging Python: Goodbye Print, Hello Debugger...

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.

Nina Zakharenko

April 09, 2020
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  1. 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"]
  2. 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
  3. COMMAND LINE DEBUGGERS ‣ pdb (in standard library) ‣ ‣

    ipdb- ipdb (via pip install ipdb) ‣ & more... @nnja
  4. GRAPHICAL DEBUGGERS ‣ pudb (graphical CLI) ‣ IDEs ‣‣ Visual

    Studio Code ‣PyCharm ‣ & others ... @nnja
  5. breakpoint() ADVANTAGES ‣ set your debugger of choice (I like

    ipdb) ‣export PYTHONBREAKPOINT=ipdb.set_trace (only in Python >= 3.7) @nnja
  6. breakpoint() ADVANTAGES environment variable that allows you skip all debug

    breakpoints $ PYTHONBREAKPOINT=0 python3.7 prod_code.py (only in Python >= 3.7) @nnja
  7. 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
  8. 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
  9. PYTHON EXTENSION FOR VS CODE ‣ 1. Download VS Code

    ‣ 2. Install Python Extension ‣ 3. Create a Debugger Configuration ‣
  10. 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
  11. 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
  12. ! 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
  13. 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
  14. ADDITIONAL RESOURCES ‣ Interactive pdb Tutorial (also in Korean) ‣

    Python 3.7’s new builtin breakpoint — a quick tour THANKS ‣ ! Thea Flowers @nnja