When Good Code Goes Bad: Tools and Techniques for Troubleshooting Plone Plone Conference 2008 David Glick Web Developer ONE/Northwest

What we're going to cover 1. Preparation for debugging 2. Debugging tools 3. 2 case studies 4. Tips & tricks

1. Preparation for debugging

2. Debugging tools

3. 2 case studies

4. Tips & tricks

Newbie programmer's reaction: Absolute terror

Experienced programmer's reaction: Absolute terror

Maybe it's a little bug...

...but who knows what's in there, really!

What could be wrong? Trivial typo Logic error Failure to consider certain input values Faulty assumptions about the state of the system Deep voodoo

Trivial typo

Logic error

Failure to consider certain input values

Faulty assumptions about the state of the system

Deep voodoo

Mental preparation

Remember: You are in control.

Remember: You are not alone.

Use the source, Luke.

Getting ready...

Don't use debugging tools in production. Security Performance

Security

Performance

Run zope in foreground mode. Buildout: $ bin/instance fg Pre-buildout: $ zopectl fg

Buildout:

$ bin/instance fg

Pre-buildout:

$ zopectl fg

Turn on verbose security. Buildout: in buildout.cfg, [instance] section: verbose-security on Pre-buildout: in zope.conf: verbose-security on security-policy-implementation python

Buildout:

in buildout.cfg, [instance] section:

verbose-security on

Pre-buildout:

in zope.conf:

verbose-security on

security-policy-implementation python

Stop ignoring errors in /error_log

Debugging tools

1. What is that thing?

Firebug (Firefox) http://tinyurl.com/2z4tvg IE Web Developer Toolbar (IE) http://tinyurl.com/iedevtoolbar WebKit (Safari) http://webkit.org Google Chrome inspector Investigating HTML, CSS, and Javascript >

Firebug (Firefox)

http://tinyurl.com/2z4tvg

IE Web Developer Toolbar (IE) http://tinyurl.com/iedevtoolbar

WebKit (Safari) http://webkit.org

Google Chrome inspector

Investigating Plone viewlets and portlets plone.app.gloworm http://tinyurl.com/gloworm

plone.app.gloworm http://tinyurl.com/gloworm

Investigating the current page context Products.Clouseau http://tinyurl.com/clouseau

Products.Clouseau http://tinyurl.com/clouseau

2. What code controls this?

Seek and ye shall find! Grep Multi-file search and replace feature in editor of choice Code indexers (etags, glimpse)

Grep

Multi-file search and replace feature in editor of choice

Code indexers (etags, glimpse)

Where is the code? From a filesystem page template: <tal:block tal:replace=”python:obj.__class__”/> (gives you the dotted path of module + class of obj) From any page template: <tal:block tal:replace=”nocall:obj”/> (gives you the class name of obj)

From a filesystem page template:

<tal:block tal:replace=”python:obj.__class__”/>

(gives you the dotted path of module + class of obj)

From any page template:

<tal:block tal:replace=”nocall:obj”/>

(gives you the class name of obj)

collective.recipe.omelette Before : After: http://tinyurl.com/collective-omelette

Before :

After:

3. What's that code doing?

Logging context.plone_log(my_var) Output will show up on console Useful for when some code is being run repeatedly and you want to make sure it's operating on the correct values

context.plone_log(my_var)

Output will show up on console

Useful for when some code is being run repeatedly and you want to make sure it's operating on the correct values

pdb: the Python debugger

pdb: the Python debugger Trigger with: import pdb; pdb.set_trace() Don't forget to remove the set_trace!

Trigger with:

import pdb; pdb.set_trace()

Don't forget to remove the set_trace!

4. What's Zope doing right now? DebugInfo page (built in): /ControlPanel/DebugInfo/manage_main in ZMI DeadlockDebugger product http://tinyurl.com/deadlockdebugger

DebugInfo page (built in): /ControlPanel/DebugInfo/manage_main in ZMI

DeadlockDebugger product http://tinyurl.com/deadlockdebugger

5. Why is this so slow ? YSlow – frontend performance http://developer.yahoo.com/yslow/ PTProfiler – page templates http://plone.org/products/ptprofiler ZopeProfiler – Python calls http://pypi.python.org/pypi/Products.ZopeProfiler

YSlow – frontend performance

http://developer.yahoo.com/yslow/

PTProfiler – page templates

http://plone.org/products/ptprofiler

ZopeProfiler – Python calls

http://pypi.python.org/pypi/Products.ZopeProfiler

What does it look like in real life? Case #1: plone_newbie4022's Quick Installer problem (from #plone, 2008-09-08)

Case #1:

plone_newbie4022's Quick Installer problem

(from #plone, 2008-09-08)

Reading a traceback module Line # method More recent Snapshot of what code is executing Doesn't include the values

Snapshot of what code is executing

Doesn't include the values

Reading a traceback (cont'd) For page template expressions Template file location The actual TAL expression that was called Location of expression within the template The actual Error message! Bonus (but irrelevant) error The Error happened here!

Common Python exceptions AttributeError e.g. obj.nonexistent_attribute ImportError e.g. import nonexistent_module IndexError e.g. my_list[42] , if my_list doesn't have >=43 elements

AttributeError

e.g. obj.nonexistent_attribute

ImportError

e.g. import nonexistent_module

IndexError

e.g. my_list[42] , if my_list doesn't have >=43 elements

Common Python exceptions KeyError e.g. my_dict['nonexistent_key'] TypeError e.g. foo = ('tuple',) + 'string' ValueError e.g. int('string')

KeyError

e.g. my_dict['nonexistent_key']

TypeError

e.g. foo = ('tuple',) + 'string'

ValueError

e.g. int('string')

Common Zope exceptions Unauthorized NotFound Redirect TraversalError ComponentLookupError – failed zope 3 lookup ConflictError – ZODB conflict

Unauthorized

NotFound

Redirect

TraversalError

ComponentLookupError – failed zope 3 lookup

ConflictError – ZODB conflict

Lessons from Case #1

The problem is sometimes (usually?) not where you think the problem is.

The problem is sometimes (usually?) not where you think the problem is.

Think carefully about both: What the code is doing What the state is of the objects in your ZODB

Think carefully about both:

What the code is doing

What the state is of the objects in your ZODB

Often you don't have to change any code to fix a bug, once you understand what is going on.

Often you don't have to change any code to fix a bug, once you understand what is going on.

What does it look like in real life? Case #2: some (only somewhat) contrived catalog trouble

Case #2:

some (only somewhat) contrived

catalog trouble

plone.reload Reload Python code without restarting Zope. Just go to /@@reload.

Reload Python code without restarting Zope.

Just go to /@@reload.

pdb commands l / list: print the code. l 42 == list line #42 w / where: print a traceback n / next: run the next command s / step: enter a method that is being called r / return: execute until the current method completes c / continue: continue execution indefinitely (end pdb session)

l / list: print the code. l 42 == list line #42

w / where: print a traceback

n / next: run the next command

s / step: enter a method that is being called

r / return: execute until the current method completes

c / continue: continue execution indefinitely (end pdb session)

advanced pdb commands b / breakpoint: b 42 == set a breakpoint on line 42 cl / clear: cl 1 == remove breakpoint #1 j / jump: j 42 == jump to line 42 u / up: move up in the call stack d / down: move down in the call stack Full pdb docs: http://www.python.org/doc/2.5.2/lib/module-pdb.html

b / breakpoint: b 42 == set a breakpoint on line 42

cl / clear: cl 1 == remove breakpoint #1

j / jump: j 42 == jump to line 42

u / up: move up in the call stack

d / down: move down in the call stack

Full pdb docs: http://www.python.org/doc/2.5.2/lib/module-pdb.html

pdb idioms pp obj – pretty-print an object dir(obj) – list an object's attributes and methods obj.__dict__ -- list an object's data attributes obj.__doc__ -- print an object's docstring args – list the arguments passed to the current method retval – print the value that will be returned from the current method !expr – force expr to be treated as a Python expression rather than a pdb command

pp obj – pretty-print an object

dir(obj) – list an object's attributes and methods

obj.__dict__ -- list an object's data attributes

obj.__doc__ -- print an object's docstring

args – list the arguments passed to the current method

retval – print the value that will be returned from the current method

!expr – force expr to be treated as a Python expression rather than a pdb command

Lessons from Case #2

If you don't have a traceback, finding the source of misbehavior can be hard . Be persistent.* * Bad Zope pun not intended.

If you don't have a traceback, finding the source of misbehavior can be hard . Be persistent.*

* Bad Zope pun not intended.

Try the most obvious things first. (Assume there's a bug in your own code, rather than in Zope/Plone.)

Try the most obvious things first. (Assume there's a bug in your own code, rather than in Zope/Plone.)

Tips and Tricks

PDBDebugMode product Automatically get a pdb whenever there is a python exception Invoke a pdb on any context via /@@pdb view Invoke a pdb on anything via /path/to/anything?pdb_runcall=1

Automatically get a pdb whenever there is a python exception

Invoke a pdb on any context via /@@pdb view

Invoke a pdb on anything via /path/to/anything?pdb_runcall=1

Debugging python scripts Use the zdb product http://www.simplistix.co.uk/software/zope/zdb from Products.zdb import set_trace; set_trace() Ensures that you can (l)ist the code of the Python script Doesn't work for form controller Python scripts (.cpy) though When stepping into calls in restricted python, you will first enter guarded_getattr, which you can (r)eturn out of and then the (n)ext call will be the one you want

Use the zdb product http://www.simplistix.co.uk/software/zope/zdb

from Products.zdb import set_trace; set_trace()

Ensures that you can (l)ist the code of the Python script

Doesn't work for form controller Python scripts (.cpy) though

When stepping into calls in restricted python, you will first enter guarded_getattr, which you can (r)eturn out of and then the (n)ext call will be the one you want

Tab key auto-completion in pdb Add the following to ~/.pdbrc: import rlcompleter pdb.Pdb.complete = rlcompleter.Completer(locals()).complete

Add the following to ~/.pdbrc:

import rlcompleter

pdb.Pdb.complete = rlcompleter.Completer(locals()).complete

Why aren't my changes coming alive? template, image & stylesheet customizations: put CSS, Javascript, KSS registries in debug mode, or at least re-save them make sure you don't have something in portal_skins/custom or portal_view_customizations that's overriding your filesystem item flush browser cache

template, image & stylesheet customizations:

put CSS, Javascript, KSS registries in debug mode, or at least re-save them

make sure you don't have something in portal_skins/custom or portal_view_customizations that's overriding your filesystem item

flush browser cache

Why aren't my changes coming alive? changes to python code or ZCML: restart Zope, or use plone.reload

changes to python code or ZCML:

restart Zope, or use plone.reload

Why aren't my changes coming alive? changes to GenericSetup profiles: re-run profile or reinstall product (don't need to restart zope) installing a new product: if not in the Products namespace, did you add a ZCML slug?

changes to GenericSetup profiles:

re-run profile or reinstall product (don't need to restart zope)

installing a new product:

if not in the Products namespace, did you add a ZCML slug?

Debugging KSS Use the FireKiss add-on for Firebug: http://tinyurl.com/firekiss Configure KSS debug log at /@@kss_devel_mode/ui Be aware that KSS will time out if you try to put a pdb set_trace in your server-side KSS action code

Use the FireKiss add-on for Firebug: http://tinyurl.com/firekiss

Configure KSS debug log at /@@kss_devel_mode/ui

Be aware that KSS will time out if you try to put a pdb set_trace in your server-side KSS action code

Common red herrings

“Not authorized to access binding.” A deferred permission error from earlier in code execution. See http://tinyurl.com/unauthorizedbinding

A deferred permission error from earlier in code execution.

See http://tinyurl.com/unauthorizedbinding

Quick Installer swallows import errors (Fixed in Plone 3.1.2)

(Fixed in Plone 3.1.2)

AttributeError: getGroups Usually means you moved the site to a new Zope, whose acl_users needs to be converted to be PAS-enabled. You can trigger that conversion by adding a brand new Plone site.

Usually means you moved the site to a new Zope, whose acl_users needs to be converted to be PAS-enabled.

You can trigger that conversion by adding a brand new Plone site.

“No traversable adapter found.” Usually a symptom of Five failing to load. Start Zope in foreground mode and watch the console for the real traceback.

Usually a symptom of Five failing to load.

Start Zope in foreground mode and watch the console for the real traceback.

Credits Cave openings, screenshots – David Glick First computer bug – US Navy / public domain Flickr users: rotten apples – alisonedunn – CC Attribution gearing up for spelunking – jarvist – CC Attribution pause button – Jobot Da Robot – CC Attribution Share Alike “ debug yourself” – joshlewis – CC Attribution NC Share Alike “ no fish” – waldopepper – CC Attribution NC These slides are licensed under the following license: Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

Cave openings, screenshots – David Glick

First computer bug – US Navy / public domain

Flickr users:

rotten apples – alisonedunn – CC Attribution

gearing up for spelunking – jarvist – CC Attribution

pause button – Jobot Da Robot – CC Attribution Share Alike

“ debug yourself” – joshlewis – CC Attribution NC Share Alike

“ no fish” – waldopepper – CC Attribution NC

These slides are licensed under the following license: Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License