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I have 2 python classes in two files.

  • file: LdapConnection, class: LdapClass(), method : getMachines(self)

    @defer.inlineCallbacks
def getMachines(self):
    c = ldapconnector.LDAPClientCreator(reactor, ldapclient.LDAPClient)
    overrides = {self.basedn: (self.serverip, 389)}
    client = yield c.connect(self.basedn, overrides=overrides)
    yield client.bind(self.binddn, self.bindpw)
    o = ldapsyntax.LDAPEntry(client, self.basedn)
    results = yield o.search(filterText=self.query)
    for entry in results:
        for i in entry.get('name'):
            self.machineList.append(i)

    yield self.machineList
    print self.machineList
    return

above print statements print all entires in the machineList

  • file:Twisted, class:Caching, method:loadSettings(self)

    @defer.inlineCallbacks 
def loadSettings(self):

    returned =  yield LdapClass().getMachines()  
    print returned

in the above class my print prints None. What Im doing wrong here?

Sraw
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Ratha
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  • I have tried to format your code but it is really broken before. So I am not sure am I right. Please check. – Sraw Oct 18 '17 at 03:52
  • Possible duplicate of [What is the result of a yield expression in Python?](https://stackoverflow.com/questions/10695456/what-is-the-result-of-a-yield-expression-in-python) – Aaron Oct 18 '17 at 03:55
  • Can you reduce your example to a [Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve)? It's difficult to get the exact output you see. Your use of yield is curious indeed. The combination of `yield` and `return` looks suspect, as does returning yielded values from functions and yielding lists rather than individual items. I'd expect looped yields or `yield from` although I realise you are using py2 which doesn't have `yield from`. – Paul Rooney Oct 18 '17 at 04:32
  • The answer to this question is included in on the other similar question you asked about this code. https://stackoverflow.com/questions/46801724/how-to-assign-a-returned-value-from-the-defer-method-in-python-twisted – Jean-Paul Calderone Oct 18 '17 at 11:01

2 Answers2

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In getMachines(), don't yield self.machineList.

In a method decorated by defer.inlineCallbacks, what yield does is yield execution until the argument (a defer.Deferred object) calls back with a value (if it's not a defer.Deferred, it'll simply continue). (It's similar to the new await keyword in Python 3.) You are using this correctly in loadSettings().

In getMachines(), you don't have a defer.Deferred; you have a list, so it continues. To return that value to the caller, call returnValue(self.machineList) at the end of the method.

Wilfredo Sánchez Vega
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Looks like your loadSettings() routine is yielding the getMachines() generator, not the results from the generator. Perhaps the former should be doing “yield from”?

Lawrence D'Oliveiro
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