[Twisted-Python] Design Pattern for Iterating Through Lists

[Ken Kinder]

I've come almost to the point of making a template for this kind of 
operation:

    d = Deferred()
    d.callback(0)

    results = []

    def doItem(void, eggs):
        return whatever(eggs)

    def processResult(result):
        results.append(result)

    for spam in list:
        d.addCallback(doItem, spam['eggs'])
        d.addCallback(processResult)

    d.addCallback(lambda _: results)
    return d

The reason I'm calling back on doItem is that lambda will evaluate its 
variables one for the iteration, causing only the first evaluation of 
spam['eggs'] to be passed for each item in the list. Is there a more 
readable/efficient way of doing this? Note that I'm not using a 
DeferredList because I want everything processed serially, not in parallel.

-Ken