This week in Launchpad’s web API
Friday, August 15th, 2008Now that the Launchpad web service API has entered beta, I’ll be posting an update every week about the improvements we make to it. This way you’ll always know what’s going on, and you’ll see when something you want to do becomes possible.
Web service improvements
This week I made one major change to the web service itself. There’s now a special top-level resource that’s an alias to “you” on Launchpad. This is a nice convenience when you’re writing scripts for yourself, but it’s practically essential if other people are going to be running your program.
Here’s how to get a reference to the person who’s running the script, using launchpadlib, our Python interface to the web service.
>>> me = launchpad.me
>>> print me.name
leonardr
If you’re not using launchpadlib, GET the service root at https://api.staging.launchpad.net/beta/, and you’ll see the URL to this resource as ‘me_link’. When you GET that URL you’ll be redirected to your own user account.
launchpadlib improvements
I spent most of my time working on launchpadlib. Apart from some bugfixes and performance improvements that you won’t even notice, I made three big improvements.
Introspection
Previously, to see what capabilities a launchpadlib object had, you had to check the reference documentation. (That documentation is two weeks out of date, by the way; we’ll be fixing that next week.) Now you can just call dir() on an object, and all of its Launchpad-derived attributes and methods will show up in the list. If you only want to see the Launchpad attributes or methods and not all the internal launchpadlib stuff, you can check lp_attributes or lp_operations. This code shows what you can do with a launchpadlib person object:
>>> me.lp_attributes
['self_link', 'resource_type_link', 'longitude', ... 'homepage_content']
>>> me.lp_operations
['addMember', ... 'setLocation']
Slices
The second new feature is the ability to slice Launchpad collections as though they were Python lists. Here’s some code that gets the 10 most recently filed bugs in Launchpad.
>>> recent_bugs = launchpad.bugs[:10]
>>> [bug.id for bug in recent_bugs]
[258042, 258041, 258040, 258039, 258038, 258037, 258036, 258033, 258032, 258030]
Previously, the only way to do this was to iterate over launchpad.bugs and insert a break statement when you’d had enough, which was very awkward.
Loading from bookmarks
The third new feature is the ability to bookmark launchpadlib objects and go back to them later, the way you can bookmark web pages in your browser. Here’s launchpadlib code to acquire a bug.
>>> a_bug = launchpad.bugs[251497]
>>> print a_bug.title
Make it possible to instantiate a resource from a URL
I can play around with that bug all I want within a Python session, but if I exit the Python session the bug will disappear. If I want to get the bug back later, I’ll need to find it again from scratch. Unless I store the bug’s unique ID (also known as its URL).
>>> print str(a_bug)
https://api.staging.launchpad.net/beta/bugs/251497
At this point I can write that string to a file or database. Later on, a different process might come online and load the string back into memory. That process can get the bug object back by passing the bug’s URL into launchpad.load().
>>> a_bug = launchpad.load("https://api.staging.launchpad.net/beta/bugs/251497")
>>> print a_bug.title
Make it possible to instantiate a resource from a URL
Pretty simple stuff–people have been saving URLs and passing them around to each other for over fifteen years. The advantage of our web service’s design is that it gives you the same power in a scripted environment.
Upcoming work
Next week I plan to spend most of my time on behind-the-scenes performance improvements. You won’t notice anything if you use launchpadlib. If you’re writing your own client, you’ll know what I’m talking about when I say “ETag support.”
Meanwhile, Edwin Grubbs will be working to expose Launchpad’s project registry through the web service.
See you next week!
