Building Web Services with Pyramid

Using Pyramid for now on

Last year, when we started to write servers apps in Python at Mozilla Services, we've built a light micro-framework on the top of WebOb and Routes. That made a lot of sense back then because all our applications were pure JSON web services --except the reCaptcha view we display when you register in Sync--

The framework just needed to route a request to a function and let us do our work in pure Python from there.

Given the nature of our apps, we did not pick an async framework for the sake of code simplicity. And with Gevent, you still can boost a synchronous app that's waiting for some I/O, by making the socket layer cooperative. IOW, making your synchronous app do some work asynchronously transparently. And that works: The Sync server uses this feature for SQL and LDAP queries, and is able to handle much more concurrent requests that way.

When we made the choice of WebOb/Routes, Pyramid was on my radar and seemed like a good option too, but was still a bit new, so we just used WebOb, knowing that a move to Pyramid would be quite easy since it's based on it too.

Today, Pyramid is quite spread and mature, and for developing Sagrada components, it makes a lot of sense to adopt it. Having Ben Bangert and Rob Miller in the team also made that choice natural : they're involved in the project so they can sneak in our crazy patches ;)

Cornice - web service builder

Building web services for Sagrada, or for any project as a matter of fact, should be as simple as possible for developers. In all the frameworks I've used in the past, it was often requiring good chunks of boiler-plate code, or I had to use some tools that were making too many choices for me. For example, we want to build REST APIs, but sometimes our APIs are not strictly REST, just REST-ish I would say :)

In the past week, we've worked on a little extension called Cornice, that tries to simplify as much as possible the usage of Pyramid to write Web Services the way we like, with the experience we had writing Sync, Account portal, Easy Setup, and all the other services that are currently running in prod.

The result is a simple class that can be used to define a service on the server, then you can declare your APIs.

Here's an extract taken from demoapp,
from collections import defaultdict

from cornice import Service



user_info = Service(name='users', path='/{username}/info')

_USERS = defaultdict(dict)



@user_info.get()

def get_info(request):

    """Returns the public information about a **user**.



    If the user does not exists, returns an empty dataset.

    """

    username = request.matchdict['username']

    return _USERS[username]



@user_info.post()

def set_info(request):

    """Set the public information for a **user**.



    You have to be that user, and *authenticated*.



    Returns *True* or *False*.

    """

    username = request.matchdict["username"]

    _USERS[username] = request.json_body

    return {'success': True}

Please don't look at what the code does, it's crappy. The _USERS stuff should be in a Pyramid registry.

But look at how I've defined my service: a Service instance for a given path on our server, followed by two functions, one for the GET, and one for the POST. By default, the APIs are returning JSON, but you can change every option Pyramid offers when you declare a view.

And once this is done, I also get for free a documentation page at /__apidocs__ by grabbing the docstrings and also looking at the various Service instance that were declared.

[image][]

Cornice is just syntaxic sugar, but we might add a few extra features late, maybe a fine-grained description of the params of each web services, so we could publish a manifest that could be introspected.

But it's good enough for people to start building Web Services for Sagrada in a standard, easy-to-read, fashion. They just need to call a config.include('cornice') in their Pyramid app, and use the Service class.

[image]: http://ziade.org/cornice-apidocs.png

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