Making a python program wait until Twisted deferred returns a value

What it seems like is you're trying to make/run multiple reactors. Everything gets attached to the same reactor. Here's how to use a DeferredList to wait for all of your callbacks to finish.

Also note that twisAmaz returns a value. That value is passed through the callbacks DeferredList and comes out as value. Since a DeferredList keeps the order of the things that are put into it, you can cross-reference the index of the results with the index of your ISBNs.

from twisted.internet import defer

def twisAmazon(contents):
    stonesoup = BeautifulStoneSoup(contents)
    ret = {}
    if stonesoup.find("mediumimage") is None:
        ret['imageurl'] = "/images/notfound.png"
    else:
        ret['imageurl'] = stonesoup.find("mediumimage").url.contents[0]
    ret['usedPdata'] = stonesoup.find("lowestusedprice")
    ret['newPdata'] = stonesoup.find("lowestnewprice")
    ret['titledata'] = stonesoup.find("title")
    ret['reviewdata'] = stonesoup.find("editorialreview")
    if stonesoup.find("asin") is not None:
        ret['asin'] = stonesoup.find("asin").contents[0]
    else:
        ret['asin'] = 'None'
    return ret

callbacks = []
for tmpISBN in isbn:  #Go through ISBN numbers and get Amazon API information for each
    callbacks.append(getPage(fetchInfo(tmpISBN)).addCallback(twisAmazon))

def printResult(result):
    for e, (success, value) in enumerate(result):
        print ('[%r]:' % isbn[e]),
        if success:
            print 'Success:', value
        else:
            print 'Failure:', value.getErrorMessage()

callbacks = defer.DeferredList(callbacks)
callbacks.addCallback(printResult)

reactor.run()

Another cool way to do this is with @defer.inlineCallbacks. It lets you write asynchronous code like a regular sequential function: http://twistedmatrix.com/documents/8.1.0/api/twisted.internet.defer.html#inlineCallbacks

First, you shouldn't put a reactor.stop() in your deferred method, as it kills everything.

Now, in Twisted, "Waiting" is not allowed. To print results of you callback, just add another callback after the first one.