Speno's Pythonic Avocado 2004/2

Teaching Twisted

I gave a short presentation at work today on the basics of Twisted. I tried to cover what I consider Twisted's core networking features: Protocols, Transports, Reactors, Factories and Deferreds.

Here's the same code I used to demonstrate the first four of those items:

from twisted.internet import protocol
from twisted.internet import reactor

class CountingEchoProtocol(protocol.Protocol):

    def dataReceived(self, data):
        self.transport.write(data)
        self.factory.incrementCount(len(data))
        data_written = self.factory.getCount()
        self.transport.write('Wrote %d bytes so far.\r\n' % data_written)

class CountingEchoFactory(protocol.ServerFactory):
   
    protocol = CountingEchoProtocol

    def __init__(self, max=24):
        self.count = 0
        self.max = max

    def incrementCount(self, length):
        self.count = self.count + length
        if self.count >= self.max:
            reactor.stop()

    def getCount(self):
        return self.count

ce_factory = CountingEchoFactory(25)
reactor.listenTCP(2323, ce_factory)
reactor.run()
print 'Wrote %d bytes total.' % ce_factory.getCount()

In prepartion for giving this informal talk, I spent about an hour or so just digging through the Twisted docs and/or the code answering my own questions. So hopefully my co-workers and I all got something from this.

Take care.

Help Wanted

My employer is looking for someone to help me out at work for a short time, maybe a month or two. Requirements including knowing your way around Python, MySQL, CGI, HTML, and UNIX. We prefer someone who can be on site. If we can't get someone soonish, then we'll probably delay the position until May.

If you are interested, drop me a line at spamfilter@macspeno.com.

Take care.

Two Python SNMP packages updated

Two python SNMP packages got updates today. First, there's Ilya Etingof's PySNMP which is now at version 3.4.1. Ilya's also broken the "example" applications out of the main package and called it pysnmp-apps-0.0.1. You can find them both here .

The second update comes from Mike Fletcher who released version 0.2.0 of his TwistedSNMP implementation. This is an SNMP handler for Twisted , which happens to use PySNMP. The new version has a mass-query program which can query a bunch of agents at once. I'm very excited to try it out in my own projects soon.

Thank you Ilya. Thank you Mike. You guys make me look good.

Popen5: useful!

I've been playing with Peter Astrand's Popen5 module lately. It's really nice and I hope that it will be accepted into Python's standard library eventually via PEP 324 .

I like this module because it allows nice and easy control over child processes. I get full control of the child's stdin, stdout, and stderr without having to do the dup dance (which I'd always have to lookup before this). And I can make an easy timeout without having to use SIGALRM.

I especially appreciate Popen5 in light of having spent way too much time tring to get a simple return value out of Twisted's utils.getProcessValue() last weekend. But that was mostly my fault.

Here's an example of using Popen5:

import popen5
import time
import os
import signal

def main():

    wait_time = 5 # seconds
    args = ['/sbin/ping', '-i', '10', 'localhost']

    outf = open('ping.out', 'w+')
    errf = open('ping.err', 'w+')

    ping = popen5.Popen(args, stdout=outf, stderr=errf)

    print 'ping started with pid ', ping.pid

    time_done = time.time() + wait_time

    while ping.poll() == -1:
        if time.time() > time_done:
            print 'bored now!'
            os.kill(ping.pid, signal.SIGINT)
            time.sleep(1)
            os.waitpid(ping.pid, os.WNOHANG)
            break
        else:
            time.sleep(1)

    for f in [outf, errf]:
        f.seek(0)
        output = f.read()
        if output:
            print 'Contents of %s:' % f.name
            print output
        
if __name__ == '__main__':
    main()

Take care.

P.S. Thanks to everyone who's left comments here. I'm learning a lot, and feel more like a member of the global Python community now. Since I won't make it to either PyCon or OSCON this year, I'm glad I have this.