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nina.to/djangocon2019
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NINA ZAKHARENKO
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GOODBYE PRINT,
HELLO DEBUGGER
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@NNJA
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LIVETWEET
#DJANGOCON
@NNJA
nina.to/djangocon2019
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whoami?
@nnja
nnja
✏
nina.to
nina.to/djangocon2019
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WHY USE
DEBUGGERS?
@nnja • nina.to/
djangocon2019
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DEMO APPLICATION
@nnja • nina.to/djangocon2019
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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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PRINT
@nnja • nina.to/djangocon2019
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A DEBUGGER HELPS YOU
EXAMINE THE STATE
OF A RUNNING PROGRAM
@nnja • nina.to/djangocon2019
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DEBUGGING
@nnja • nina.to/djangocon2019
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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
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(THIS IS MY WAY)
NOT ONE "RIGHT" WAY
@nnja • nina.to/djangocon2019
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TYPES OF
DEBUGGERS
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CLI
‣ pdb (in standard library)
‣ ‣ ipdb- ipdb (via pip install
ipdb)
‣ & more...
@nnja • nina.to/djangocon2019
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@nnja
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GRAPHICAL DEBUGGERS
‣ pudb (graphical CLI)
‣ IDEs
‣‣ Visual Studio Code
‣PyCharm
‣ & others ...
@nnja • nina.to/djangocon2019
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No content
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BREAKPOINTS
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PYTHON 3.7?
USE breakpoint()
@nnja • nina.to/djangocon2019
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breakpoint() ADVANTAGES
‣ set your debugger of choice
(I like ipdb)
‣export PYTHONBREAKPOINT=ipdb.set_trace
(only in Python >= 3.7)
@nnja • nina.to/djangocon2019
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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
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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
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DEBUGGER
FUNDAMENTALS
@nnja • nina.to/djangocon2019
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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/djangocon2019
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@nnja • nina.to/djangocon2019
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DEBUGGERS
IN IDES
@nnja • nina.to/djangocon2019
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PYTHON EXTENSION FOR VS CODE
‣ 1. Download VS Code
‣ 2. Install Python Extension
‣ 3. Create a Debugger Configuration
‣
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VISUAL BREAKPOINTS
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WHEN TO
USE WHAT?
@nnja • nina.to/djangocon2019
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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
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TIPS & TRICKS
@nnja • nina.to/djangocon2019
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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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⚡
NEW!
DEBUGGING
JUPYTER NOTEBOOKS
IN VS CODE
nina.to/debug_jupyter
@nnja • nina.to/djangocon2019
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!
GOTCHAS
@nnja • nina.to/djangocon2019
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!
DON'T LEAVE BREAKPOINTS
IN PRODUCTION CODE!
@nnja • nina.to/djangocon2019
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!
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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!
WRAPPING UP
@nnja • nina.to/djangocon2019
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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
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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
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THANKS!
@NNJA
SLIDES:
nina.to/djangocon2019
PYTHON @ MICROSOFT:
aka.ms/djangocon2019