[Twisted-Python] Looping

Robert Hancock hancock.robert at gmail.com
Mon Jan 5 23:01:16 EST 2009

I understand how the deferreds can create concurrency, but I still
cant' figure out how to get the process to loop correctly

I changed the code to use multiple deffereds, but I feel I'm missing a
basic architectural design on how to get the process to run in a loop.
 Any help would be greatly appreciated.

Case 1
If I execute if with:

If executes perfectly, one time.  Or from a loop in a shell script it
also runs fine multiple times.

I would like to perform the same function every 30 seconds from within
the script, but when I try:
    while True:

Case 2
It executes twice and hangs, and when you hit Ctrl-C the traceback is:

  File "main_rss.py", line 94, in <module>
  File "/usr/local/python26/lib/python2.6/site-packages/Twisted-8.2.0-py2.6-linux-x86_64.egg/twisted/internet/base.py",
line 1128, in run
  File "/usr/local/python26/lib/python2.6/site-packages/Twisted-8.2.0-py2.6-linux-x86_64.egg/twisted/internet/base.py",
line 1137, in mainLoop
--- <exception caught here> ---
  File "/usr/local/python26/lib/python2.6/site-packages/Twisted-8.2.0-py2.6-linux-x86_64.egg/twisted/internet/base.py",
line 729, in runUntilCurrent
    f(*a, **kw)
  File "/usr/local/python26/lib/python2.6/site-packages/Twisted-8.2.0-py2.6-linux-x86_64.egg/twisted/internet/base.py",
line 527, in stop
    "Can't stop reactor that isn't running.")
twisted.internet.error.ReactorNotRunning: Can't stop reactor that isn't running.

Case 3
I tried th task.LoopingCall() example from the manual and wrote:
    rf = RSSFeedStorage(GROUPS)
    l = task.LoopingCall(rf.refreshAllFeeds())
[commented out reactor.stop in sto_working()]

and it raises the following exception, I assume because the function
returns a deferred list.

exceptions.AttributeError: DeferredList instance has no __call__ method

==== Code ======

import os
import time
import xml.sax.saxutils

from twisted.internet import reactor, defer, protocol, task
from twisted.web import client

GROUPS = { 'yahoo' : 'http://finance.yahoo.com/rss/usmarkets',
           'npr': 'http://www.npr.org/rss/rss.php?id=1006',
RSYNC_DIR = '/local/apps/rdretrvl/rdsync/rssfeed'
escape_dict = {'/': '_'}

class RssFeed(object):

    def __init__(self, groupName, feedUrl):
        self.refreshRate = 10
        self.title = ''
        self.groupName = groupName
        self.feedUrl = feedUrl
        self.articles = []
        self.articlesById = {}
        self.lastRefreshTime = 0
        self.refreshing = None

    def refreshIfNeeded(self):
        timeSinceRefersh = time.time() - self.lastRefreshTime
        if timeSinceRefersh > self.refreshRate:
            if not self.refreshing:
                self.refreshing = client.getPage(self.feedUrl).addCallback(
            d = defer.Deferred()
            return d
            return defer.succeed(None)

    def _gotFeedData(self, data):
        print "Loaded feed data from %s" % self.feedUrl
        self.refreshing = None
        self.lastRefreshTime = time.time()
        # write to rsync directory
        name = xml.sax.saxutils.escape(self.feedUrl, escape_dict)
            fnout = os.path.join(RSYNC_DIR, name)
            fout = open(fnout, 'w')
        except IOError, e:
            print e
            #log.error('Opening %s: %s' % (fnout, e))

            #log.info('Wrote %s.' % fnout)
            print 'Wrote %s.' % fnout
        except IOError, e:
            print e
            #log.error('Wrting to %s: %s' % (fnout, e))

    def _getDataFailed(self, failure):
        print 'Failed to load RSS data from %s: %s' % (self.feedUrl,
        self.refreshing = None
        return failure

class RSSFeedStorage(object):

    def __init__(self, feeds):
        self.feeds = {}
        for groupName, url in feeds.iteritems():
            self.feeds[groupName] = RssFeed(groupName, url)

    def refreshAllFeeds(self):
        refreshes = [feed.refreshIfNeeded() for feed in self.feeds.values()]
        return defer.DeferredList(refreshes).addCallback(self.stop_working).addErrback(self.handleError)

    def stop_working(self, data):
        print 'Reactor stopped'

    def handleError(self, failure):
        print failure

if __name__ == "__main__":

          {execution code goes here]

On Mon, Jan 5, 2009 at 11:53 AM, Drew Smathers <drew.smathers at gmail.com> wrote:
> On Sun, Jan 4, 2009 at 11:23 PM, Robert Hancock
> <hancock.robert at gmail.com> wrote:
>>> How many urls are in url_tuples?
>> 4 - 32
>>> Is there a reason why you're using just one deferred?
>> What is the advantage of using more?
> Concurrency.
> -Drew
> _______________________________________________
> Twisted-Python mailing list
> Twisted-Python at twistedmatrix.com
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