About

Corduroy provides a python-friendly wrapper around CouchDB’s HTTP-based API. Behind the scenes it hooks into the asynchronous i/o routines from your choice of Tornado or the Requests & Gevent modules.

Using corduroy you can query the database without blocking your server’s event loop, making it ideal for CouchApp micro-middleware or scripted batch operations.

Usage

As a real world(ish) example of working with Corduroy, consider this pair of Tornado event handlers which update a url-specifed document then query a view. The first uses explicit callbacks to resume execution after each response from the database is received:

db = Database('players')
class RankingsUpdater(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def post(self, player_id):
        self.new_score = int(self.request.body)
        db.get(player_id, callback=self.got_player)

    def got_player(doc, status):
        doc.score = self.new_score
        db.save(doc, callback=self.saved_player)

    def saved_player(conflicts, status):
        db.view('leaderboard/highscores',
                 callback=self.got_highscores)

    def got_highscores(rows, status):
        self.write(json.dumps(rows))
        self.finish()

An alternative syntax is available (when using Tornado) through the use of the @relax decorator. Instead of defining callbacks for each database operation, the library can be called as part of a yield expression.

Tornado’s generator module will intercept these yields and provide a callback automatically. The result is code that looks quite sequential but will still execute asyncronously:

class RankingsUpdater(tornado.web.RequestHandler):
    @relax
    def post(self, player_id):
        # update this player's score
        doc = yield db.get(player_id)
        doc.score = int(self.request.body)
        yield db.save(doc)

        # return the new rankings
        highscores = yield db.view('leaderboard/highscores')
        self.write(json.dumps(highscores))
        self.finish()

For a gentle introduction to Corduroy (and CouchDB in general), take a look at the Guide. Documentation for all of Corduroy’s module-level classes can be found in the Reference section.

Installation

tar xvzf corduroy-0.9.0.tar.gz
cd corduroy-0.9.0
python setup.py install

pip install corduroy tornado

pip install corduroy tornado pycurl

env ARCHFLAGS="-arch x86_64" pip install pycurl

pip install corduroy requests gevent

pip install corduroy requests

License

Corduroy is released under the BSD license. Use it freely and in good health.

Acknowledgments

Corduroy is derived from Christopher Lenz’s excellent couchdb-python module and inherits much of its API (and most of its test cases) from that codebase. It is also indebted to Eric Naeseth’s mind-expanding Swirl library which first acquainted me with the idea of using generators to simulate sequential code.