human
I wrote the below code

    def callback(iq):
        '\n                                Handle    iq    response    by    firing    associated    deferred.\n                                '
        if getattr(iq, 'handled', False):
            return
        try:
            d = xs.iqDeferreds[iq['id']]
        except KeyError:
            pass
        else:
            del xs.iqDeferreds[iq['id']]
            iq.handled = True
            if (iq['type'] == 'error'):
                d.errback(error.exceptionFromStanza(iq))
            else:
                d.callback(iq)
    def disconnected(_):
        "\n                                Make    sure    deferreds    do    not    linger    on    after    disconnect.\n\n                                This    errbacks    all    deferreds    of    iq's    for    which    no    response    has    been\n                                received    with    a    L{ConnectionLost}    failure.    Otherwise,    the    deferreds\n                                will    never    be    fired.\n                                "
        iqDeferreds = xs.iqDeferreds
        xs.iqDeferreds = {}
        for d in iqDeferreds.itervalues():
            d.errback(ConnectionLost())
    xs.iqDeferreds = {}
    xs.iqDefaultTimeout = getattr(xs, 'iqDefaultTimeout', None)
    xs.addObserver(xmlstream.STREAM_END_EVENT, disconnected)
    xs.addObserver('/iq[@type="result"]', callback)
    xs.addObserver('/iq[@type="error"]', callback)
    directlyProvides(xs, ijabber.IIQResponseTracker)

What's a good function header?
assistant
#Here's a good function header.

def upgradeWithIQResponseTracker(xs):