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
   

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2. whoami?
   @nnja
   nnja
   ✏
   nina.to
   nina.to/au19
   

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3. LIVETWEET
   #PYCONAU
   @NNJA
   nina.to/au19
   

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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
   

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5. (THIS IS MY WAY)
   NOT ONE "RIGHT" WAY
   @nnja • nina.to/au19
   

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6. WHY USE
   DEBUGGERS?
   @nnja • nina.to/au19
   

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7. DEMO APPLICATION
   @nnja • nina.to/au19
   

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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"]
   

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9. PRINT
   @nnja • nina.to/au19
   

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10. A DEBUGGER HELPS YOU
    EXAMINE THE STATE
    OF A RUNNING PROGRAM
    @nnja • nina.to/au19
    

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11. DEBUGGING
    @nnja • nina.to/au19
    

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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
    

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13. TYPES OF
    DEBUGGERS
    @nnja • nina.to/au19
    

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14. CLI
    ‣ pdb (in standard library)
    ‣ ‣ ipdb- ipdb (via pip install
    ipdb)
    ‣ & more...
    @nnja • nina.to/au19
    

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15. @nnja
    

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16. GRAPHICAL DEBUGGERS
    ‣ pudb (graphical CLI)
    ‣ IDEs
    ‣‣ Visual Studio Code
    ‣PyCharm
    ‣ & others ...
    @nnja • nina.to/au19
    

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18. BREAKPOINTS
    @nnja • nina.to/au19
    

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19. USE breakpoint()
    IN PYTHON 3.7
    @nnja • nina.to/au19
    

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20. breakpoint() ADVANTAGES
    ‣ set your debugger of choice
    (I like ipdb)
    ‣set: PYTHONBREAKPOINT=ipdb.set_trace
    @nnja • nina.to/au19
    

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21. breakpoint() ADVANTAGES
    environment variable that
    allows you skip all debug
    breakpoints
    $ PYTHONBREAKPOINT=0 python3.7 prod_code.py
    @nnja • nina.to/au19
    

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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
    

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23. DEBUGGER
    FUNDAMENTALS
    @nnja • nina.to/au19
    

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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)
    @nnja • nina.to/au19
    

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26. DEBUGGERS
    IN CLIS
    IN ACTION
    @nnja • nina.to/au19
    

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27. DEBUGGERS
    IN IDES
    @nnja • nina.to/au19
    

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28. PYTHON EXTENSION FOR VS CODE
    ‣ 1. Download VS Code
    ‣ 2. Install Python Extension
    ‣ 3. Create a Debugger Configuration
    ‣
    

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29. VISUAL BREAKPOINTS
    @nnja • nina.to/au19
    

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30. DEMO
    @nnja • nina.to/au19
    

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31. WHEN TO
    USE WHAT?
    @nnja • nina.to/au19
    

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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
    

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33. TIPS & TRICKS
    @nnja • nina.to/au19
    

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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
    

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35. BONUS:
    DEBUGGING
    JUPYTER NOTEBOOKS
    IN VS CODE
    !
    : aka.ms/pyblog
    @nnja • nina.to/au19
    

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36. !
    GOTCHAS
    @nnja • nina.to/au19
    

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37. !
    DON'T LEAVE BREAKPOINTS
    IN PRODUCTION CODE!
    @nnja • nina.to/au19
    

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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
    

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39. !
    WRAPPING UP
    @nnja • nina.to/au19
    

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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
    

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41. THANKS!
    @NNJA
    SLIDES:
    nina.to/au19
    PYTHON @ MICROSOFT:
    aka.ms/au19py
    

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