Lintel Technologies: InlineCallbacks

Twisted features a decorator named inlineCallbacks which allows you to work with deferreds without writing callback functions.

This is done by writing your code as generators, which yield deferreds instead of attaching callbacks.

Consider the following function written in the traditional deferred style:

import txredisapi as redis

from twisted.internet import defer
from twisted.internet import reactor

def main():
    rc = redis.Connection()
    print rc
    rc.addCallback(onSuccess)
    rc.addErrback(onFail)


def onSuccess(result):
    print "Success : "
    print result


def onFail(result):
    print "Fail : "
    print result


if __name__ == '__main__':
    main()
    reactor.run()

using inlineCallbacks, we can write this as:

from twisted.internet.defer import inlineCallbacks

import txredisapi as redis

from twisted.internet import defer
from twisted.internet import reactor


@defer.inlineCallbacks
def main():
    rc = yield redis.Connection()
    print rc

    yield rc.set("abc", "pqr")
    v = yield rc.get("abc")
    print "value : ", repr(v)

    yield rc.disconnect()


if __name__ == "__main__":
    main()
    reactor.run()

Instead of calling addCallback on the deferred returned by redis.Connection, we yield it. this causes Twisted to return the deferred‘s result to us.

Though the inlineCallbacks looks like synchronous code, which blocks while waiting for the request to finish, each yield statement allows other code to run while waiting for the deferred being yielded to fire.

inlineCallbacks become even more powerful when dealing with complex control flow and error handling.

The post InlineCallbacks appeared first on Lintel Technologies Blog.