from twisted.internet import reactor
from twisted.web.client import downloadPage
import sys
d = downloadPage(sys.argv[1], "foo")
def printValue(value):
    print "done"
    reactor.stop()
def printError(error):
    print "an error occured", error
    reactor.stop()
d.addCallbacks(callback=printValue, errback=printError)
reactor.run()