[Twisted-Python] t.i.task.Cooperator & inlineCallbacks mashup

Phil Mayers p.mayers at imperial.ac.uk
Wed Nov 2 10:01:19 EDT 2011

On 02/11/11 12:39, Itamar Turner-Trauring wrote:
> On Wed, 2011-11-02 at 11:24 +0000, Phil Mayers wrote:
>> I only just noticed today that if a generator passed to a
>> CooperativeTask does:
>>     result = yield some_deferred()
>> ...it doesn't work, because CooperativeTask doesn't .send() the result
>> of the deferred bacn into the generator.
>> Is this intentional? If not, would that behaviour be desirable? It seems
>> like it would be a useful pattern to me.
> Could you give an example snippet? I don't really understand the
> question, sorry.

I meant this:

from twisted.internet import task, reactor, defer

def dowork(n):
     d = defer.Deferred()
     result = 'waited %i' % (n,)
     reactor.callLater(n, d.callback, result)
     return d

def work():
     for i in (1,2,3):
         rv = yield dowork(i)
         print rv




rather than

waited 1
waited 2
waited 3

i.e. the iterator that is yielding deferreds doesn't "see" the results 
emerge from the "yield" in the same way inlineCallbacks do.

Obviously it's pretty trivial to get at the results:

   holder = {}
   def cb(r):
     holder['result'] = r
     return r
   yield dowork(i).addCallback(cb)
   print holder['result']

But the essential point I was missing is that Cooperator is for general 
purpose iterators, not just generators.

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