Simon Willison’s Weblog

snoop. Neat Python debugging utility by Alex Hall: snoop lets you “import snoop” and then add “@snoop” as a decorator to any function, which causes that function’s source code to be output directly to the console with details of any variable state changes that occur while it’s running.

I didn’t know you could make a Python module callable like that—turns out it’s running “sys.modules[’snoop’] = snoop” in the __init__.py module! # 31st January 2024, 6:19 pm

github-debug.com (via) This is a neat trick: GitHub have a dedicated site for their support engineers to send you to if you can’t connect to them. The site tests download speeds from their various domains and then lets you click a button to have GitHub run a traceroute/ping from their servers to your detected IP address and output the results (use devtools to spy on their API method for doing this). Then you can paste the results into a message to their support team. Turns out fastly-debug.com and dropbox-debug.com implement a similar pattern for those services as well. # 10th October 2018, 7:32 pm

Appending the request URL to SQL statements in Django. A clever frame-walking monkey-patch which pulls the most recent HttpRequest object out of the Python stack and adds the current request.path to each SQL query as an SQL comment, so you can see it in debugging tools such as slow query logs and the PostgreSQL “select * from pg_stat_activity” query. # 2nd June 2010, 9:09 am

Fun with TextMate and PDB. TextMate bookmarks (against lines in a file) are stored as OS X extended attributes, which can be accessed from Python using the xattr module. Here’s a clever piece of code that uses bookmarks to set breakpoints in the command-line pdb debugger. # 23rd March 2010, 9:48 am

Presenting django-devserver, a better runserver. I really like this—it’s a Django management command (./manage.py rundevserver) which adds SQL logging and cache access summaries to the console output of Django’s local development server. It solves a similar set of problems to the debug toolbar, but requires slightly less setup and doesn’t inject additional HTML in to your pages. You can add your own custom modules to it as well. # 10th February 2010, 11:33 am

Debugging in Python. The missing manual for Python’s powerful pdb debugger. # 18th November 2009, 12:34 pm

Deep Tracing of Internet Explorer. dynaTrace Ajax looks like an awesome tool. For once, Internet Explorer has a development tool that other browsers can be jealous of. # 18th November 2009, 8:06 am

django-debug-toolbar. The new panel styling for the Django debug toolbar is really slick—here’s a neatly produced screencast demonstrating it (with Gypsy Jazz accompaniment). # 21st September 2009, 6:36 pm

Debugging Django in Production Revisited. Eric Holscher expands his show-technical-errors-to-superusers middleware to only show them to users in the group named “Technical Errors”. # 7th September 2009, 5:21 am

Why I don’t love JavaScript’s Module Pattern. Jonathan Snook points out that the module pattern (where private functionality is hidden in a closure and only public methods are revealed to outside scopes) makes code a lot harder to debug. I use the module pattern for pretty much everything, not because I want to keep stuff private but more to avoid any chance of leaking out in to the global namespace. If I need to debug a value I temporarily assign it as a property on the global window object. # 30th April 2009, 7:59 pm

Finding and fixing memory leaks in Python. Using Dozer, a clever piece of WSGI middleware which displays sparklines of Python object counts and allows you to introspect them, using the gc module under the hood. # 22nd April 2009, 12:16 pm

Announcing django-viewtools. A really excellent idea—run ./manage.py viewtools --pdb /path/on/site/ to debug a view in your Django project that is raising an error using the Python debugger, or use --profile to run the full request cycle for that URL through the profiler. # 17th February 2009, 9:35 pm

ReferenceError: console is not defined. Since Firebug 1.2 you need to call window.loadFirebugConsole() in order for console.log and friends to work. # 23rd December 2008, 10:22 pm

Introducing the Django Debug Toolbar. Another project inspired by DjangoCon: a component based debugging toolbar for Django. I like the architecture so far. # 21st September 2008, 6:32 pm

Django snippets: server with debugging backdoor. Six lines of code that uses spawning to fire up a Django server on port 8000 and a remote interactive interpreter backdoor on port 8001, so you can interogate the state of your server within the same process. # 8th September 2008, 10:15 pm

Super User Conditional Page Exception Reporting. The name is almost as long as the code snippet: this serves Django’s debug page to logged in super-users, falling back to the default 500 template for everyone else. # 31st July 2008, 9:06 pm

Firebug Lite 1.2 (via) Huge upgrade to the IE/Opera/Safari bookmarklet version of Firebug—it now has DOM element inspection, XHR tracking and an interactive console, among other features. # 27th July 2008, 9:30 am

Debugging Django, a slidecast. I used SlideShare’s slidecast tool for the first time to synchronize audio of my Django London User Group talk with the slides. The talk included several live demos which aren’t represented in the slides so it’s a bit piecemeal in places. # 25th May 2008, 2:47 pm

modswgi: Debugging Techniques. mod_wsgi is excellent software, and the documentation is equally superb. I used these instructions recently to run the Python debugger inside a running instance of Apache, which helped my track down some import errors that weren’t occurring with Django’s development server. # 25th May 2008, 1:34 pm

Firebug Command Line API. Another thing I didn’t know about Firebug: you can set a breakpoint at the start of a function with “debug(fn)” and log all calls to it with “monitor(fn)”. # 16th May 2008, 12:14 pm

Opera Dragonfly. Opera’s new Firebug-style developer console. Out in alpha and it shows (slow to load and the interactive console leaves a lot to be desired) but still looks incredibly promising, especially the remote debugging tools for working with Opera on phones and games consoles. # 6th May 2008, 7:04 pm

Advanced JavaScript Debugging Techniques. There’s more to JavaScript debugging than just Firebug. # 4th April 2008, 7:51 am

Firebug + Dijit tips. News to me: Firebug has a magic $1 variable which corresponds to the currently selected node. Very handy. # 17th March 2008, 2:08 am

DebugBar. Suggested at BarCamp London 3 as a useful tool for developing with IE; apparently includes a great JavaScript debugger. # 25th November 2007, 10:32 am

jQuery Logging (via) Brilliant four line jQuery plugin that lets you insert Firebug console.log() calls directly in to chains. # 19th October 2007, 12:52 pm

XRAY now works in IE. Westciv’s smart CSS debugging bookmarklet now works in IE 6. # 21st August 2007, 8:07 am