Posts tagged "twisted" « SaltyCrane Blog

Twisted web POST example w/ JSON

Date: 2010-08-25 | Modified: 2010-10-09 | Tags: concurrency, python, twisted

This is an example of a simple asynchronous Python web server using Twisted. This is a copy of Jp Calderone's Twisted Web in 60 seconds: handling POSTs example modified to accept a JSON payload in the POST request instead of form data. It also uses his Simple Python Web Server example to run the web server as a daemon with twistd.

`webserver.py`

"""
http://jcalderone.livejournal.com/49707.html
http://labs.twistedmatrix.com/2008/02/simple-python-web-server.html

usage:
        $ twistd -y webserver.py
"""


from pprint import pprint
from twisted.application.internet import TCPServer
from twisted.application.service import Application
from ...

Quick notes on trying the Twisted websocket branch example

Date: 2010-05-24 | Modified: 2010-05-25 | Tags: concurrency, python, twisted | 4 Comments

Here are my quick notes on trying out the websocket example in Twisted's websocket branch. The documentation is here. The Twisted ticket is here. This came about after some conversation with @clemesha on Twitter.

(A Web Socket is a new, still-in-development technology, introduced in HTML5, and may be used for real-time web applications. It provides a simple (maybe better) alternative to existing Comet technology.)

(Note: The WebSocket API is still changing. Google Chrome supports (a version of) it. Firefox as of version 3.6, does not support it yet.)

(I am no expert on Web Sockets. I just think ...

Running a Twisted Perspective Broker example with twistd

Date: 2008-10-27 | Tags: concurrency, python, twisted | 1 Comment

I've been using Twisted's Perspective Broker to manage networking for my Python program. Perspective Broker allows me to run a Python program on a remote machine and perform remote method calls on an object in the Python program. It also allows me to serialize objects and transfer them over TCP.

Once I got a Perspective Broker server and client running, I wanted to create a "Twisted Application" and run it using twistd, the Twisted Daemon. Two major options are: creating a .tac file and creating a twistd plugin. Below, I show the steps I took to create a ...

Twisted links

Date: 2008-10-21 | Modified: 2009-03-18 | Tags: concurrency, python, twisted | 2 Comments

Twisted tutorials

Twisted - hello, asynchronous programming
by Jesse Noller, February 11, 2009
Overview of Twisted concepts
Twisted inlineCallbacks and deferredGenerator
by Marcin Kasperski, August 13, 2008
Examples comparing raw deferreds, deferredGenerator, and inlineCallbacks.
Async Batching with Twisted: A Walkthrough
by Duncan McGreggor, June 20, 2008
This article features 8 easy to understand examples demonstrating Deferreds, callbacks, DeferredLists, DeferredSemaphores, and task.Cooperator.
Concurrency with Python, Twisted, and Flex
by Bruce Eckel, May 3, 2008
Grokking Twisted
by Bruce Eckel, April 15, 2006
Event-Driven Programming with Twisted and Python
Linux Journal, January 26, 2005
The Twisted Matrix Framework: Part One, Understanding Asynchronous ...

Can't block for a Deferred in Twisted

Date: 2008-10-20 | Modified: 2008-10-27 | Tags: concurrency, python, twisted

Despite the existence of the promising waitForDeferred/deferredGenerator and the newer inlineCallbacks, it appears there is no way to block while waiting for a Deferred. Brian Granger described the problem on the Twisted mailing list:

I have a function that returns a Deferred. I need to have the result of this Deferred returned in a (apparently) blocking/synchronous manner:
def myfuncBlocking():
  d = myfuncReturnsDeferred()
  ...
  result =

  return result
I need to be able to call this function like:
result = myfuncBlocking()
The question is how to get the result out of the Deferred() and make it *look* like myfuncBlocking() has blocked.

glyph provided ...

Running functions periodically using Twisted's LoopingCall

Date: 2008-10-14 | Modified: 2010-09-20 | Tags: concurrency, python, twisted | 6 Comments

Twisted is pretty cool-- it is very powerful, but I haven't had the easiest time learning it. Here is a simple example that runs a couple functions periodically (at different rates) using LoopingCall.

For more information, here are the Twisted docs for LoopingCall.

from datetime import datetime
from twisted.internet.task import LoopingCall
from twisted.internet import reactor

def hyper_task():
    print "I like to run fast", datetime.now()

def tired_task():
    print "I want to run slowly", datetime.now()

lc = LoopingCall(hyper_task)
lc.start(0.1)

lc2 = LoopingCall(tired_task)
lc2.start(0.5)

reactor.run()

Results:

I like to run ...

Notes on parallel processing with Python and Twisted

Date: 2008-09-12 | Modified: 2008-10-27 | Tags: concurrency, python, twisted

Twisted is a networking engine written in Python, that among many other things, can be used to do parallel processing. It is very big, though, so I had a hard time finding what I needed. I browsed through the Twisted Documentation and the Twisted O'Reilly book. There is also a Recipe in the Python Cookbook. However, I found Bruce Eckel's article, Concurrency with Python, Twisted, and Flex to be the most helpful. (See also Bruce Eckel's initial article on Twisted: Grokking Twisted)

Here are my notes on running Bruce Eckel's example. I removed the Flex part ...