PDB LIKE A PROPHILIP BAUER

@StarzelDe

pbauer

THE BASICS

PHILIP BAUER: PDB LIKE A PRO PYCON.DE 2016

The Basics

▸ l[ist]List source code for the current file

▸ n[ext]Continue execution until the next line

▸ s[tep] Execute the current line, stop at the first possible occasion

▸ r[eturn] Continue execution until the current function returns

▸ c[ontinue] Continue execution, only stop when a breakpoint is encountered

PHILIP BAUER: PDB LIKE A PRO PYCON.DE 2016

The Basics II

▸ w[here] Show stack trace. Recent frame at bottom

▸ u[p] Move to older frame in stack trace

▸ d[own] Move to newer frame in stack trace

▸ b[reakpoint] Set a new breakpoint. tbreak Temporary breakpoint

▸ a[rgs]Print the argument list of the current function.

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Some Enhancements

▸ pdb++

▸ ipdb

▸ bpdb

▸ pudb

▸ and…

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pdb in python 3.2+

▸ ll | longlist List all source code for the current function or frame.

▸ sourceTry to get source code for the given object and display it.

▸ …

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ipdb

▸ + features

▸ - dependencies

▸ - weird sqllite

▸ - need to use ``import ipdb; ipdb.set_trace()``

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pudb

▸ + features

▸ +/- UI

▸ - need to use import pudb; pudb.set_trace()

TEXT

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▸ it’s actually called pdbpp

▸ + features

▸ + no problematic dependencies

▸ + drop-in-replacement

▸ - needs configuration to not break readline

pdb++

DEMO PDB++

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pdb++

▸ you’ll need a file ~/.fancycompleterrc.py

pdb++

▸ Syntax highlighting

▸ ll | longlistList all source code for the current function or frame.

▸ track EXPRESSION

▸ display EXPRESSION

▸ source EXPRESSION

▸ obj?

▸ obj.__class__??

▸ Sticky mode

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Give pdb++ a try!

The person you trust

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INTROSPECTION

INTROSPECTION

python stuff you should know

▸ dir(obj) - bäh!

▸ help(obj)

▸ help(obj.__class__)

▸ pp locals()

▸ obj.__dict__

▸ obj.__class__.__dict__

▸ pp dict(obj.__class__.__dict__)

INTROSPECTION

the inspect module

▸ It’s what is used by other nice tools

▸ import inspect

▸ print inspect.getsource(obj.__class__)

▸ inspect.getmro(obj.__class__)

ADVANCED TIPS

▸ break if some condition applies

▸ very useful in loops

▸ you need it in try/except blocks (e.g. indexing)

TIPS AND TRICKS

Conditional Breakpoints

TIPS AND TRICKS

debug

▸ Call any code and step into it with a pdb in a pdb

▸ You need to step into it after calling it!

▸ (Pdb++) self.context<Document at /Plone/startseite> (Pdb++) debug self.context.canSetLayout() ENTERING RECURSIVE DEBUGGER ((Pdb++)) s--Call--[2] >[…]/Products/CMFDynamicViewFTI/browserdefault.py(183)canSetLayout() ((Pdb++)) ll 183 -> @security.public 184 def canSetLayout(self): 186 mtool = getToolByName(self, 'portal_membership')

DEMO DEBUG

▸ Whenever there is a traceback you end up in a pdb!

▸ try: run_your_stuff() except: import pdb; pdb.set_trace()

▸ Plone: Products.PDBDebugMode

▸ Disable when migrating/reindexing

TIPS AND TRICKS

Post-Mortem Debugging

▸ Drops you in a pdb whenever a test fails or errors

▸ Zope/Plone: bin/test -D pytest & nosetest: pytest / nosetest --pdb unittest: need to wrap in try/except

▸ Test-Driven Debug-Driven Development

TIPS AND TRICKS

Post-Mortem Testing

▸ add a config-file ~/.pdbrc

▸ alias inspect import inspect; print inspect.getsource(%1)

▸ alias help !print help(%1)

TIPS AND TRICKS

Customize your pdb

TEXT

Sentry

▸ Collect tracebacks from production-environments

▸ The traceback includes all arguments for all stacks

▸ OpenSource / Django

▸ github.com/getsentry/sentry

▸ Available as a service: sentry.io

▸ starzel.de is working on a DebOps/Ansible role for Sentry

SUMMARY

SUMMARY

What to take away

▸ learn the basics

▸ try pdb++

▸ learn introspection

▸ try debug callable()

▸ use post-mortem-debugging

▸ always use pretty-print

▸ use Sentry to debug errors on production

QUESTIONS

Philip Bauer

@StarzelDe

pbauer

All Fotos by Philip Bauer. Taken in Boothbay, Maine October 2016