human
I wrote the below code

    def _timeout():
        deferred.cancel()
    delayed_timeout = reactor.callLater(timeout_sec, _timeout)
    if (reason is not None):
        def maybe_replace_reason(passthrough):
            if delayed_timeout.active():
                return passthrough
            return Failure(reason)
        deferred.addErrback(maybe_replace_reason)
    def abort_timeout(passthrough):
        if delayed_timeout.active():
            delayed_timeout.cancel()
        return passthrough
    deferred.addBoth(abort_timeout)
    return deferred

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

def timeout(reactor, deferred, timeout_sec, reason=None):