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An asynchronous CouchDB client library

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README.rst

Corduroy · asynchronous upholstery

project: http://samizdat.cc/corduroy
code: http://github.com/samizdatco/corduroy

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 asynchronously:

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

Automatic Installation

Corduroy can be found on PyPi and can be installed with your choice of pip or easy_install.

Manual Installation

Download corduroy-0.9.1.tar.gz or clone the repository:

tar xzf corduroy-0.9.1.tar.gz
cd corduroy-0.9.1
python setup.py install

Dependencies

If you’re writing a Tornado app, Corduroy can use its pure-python HTTP client by installing with:

pip install corduroy tornado

Or if you’d prefer the libcurl-based client (which supports pooling and other niceties), use:

pip install corduroy tornado pycurl

If pycurl complains (I’m looking at you, OS X), try:

env ARCHFLAGS="-arch x86_64" pip install pycurl

Gevent users can install with:

pip install corduroy requests gevent

The library can also be used with plain-old blocking i/o:

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.

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