from twisted.internet import reactor, error

def listen_tcp(portrange, host, factory):
    """Like reactor.listenTCP but tries different ports in a range."""
    assert len(portrange) <= 2, "invalid portrange: %s" % portrange
    if not hasattr(portrange, '__iter__'):
        return reactor.listenTCP(portrange, factory, interface=host)
    if not portrange:
        return reactor.listenTCP(0, factory, interface=host)
    if len(portrange) == 1:
        return reactor.listenTCP(portrange[0], factory, interface=host)
    for x in range(portrange[0], portrange[1]+1):
        try:
            return reactor.listenTCP(x, factory, interface=host)
        except error.CannotListenError:
            if x == portrange[1]:
                raise


class CallLaterOnce(object):
    """Schedule a function to be called in the next reactor loop, but only if
    it hasn't been already scheduled since the last time it ran.
    """

    def __init__(self, func, *a, **kw):
        self._func = func
        self._a = a
        self._kw = kw
        self._call = None

    def schedule(self, delay=0):
        if self._call is None:
            self._call = reactor.callLater(delay, self)

    def cancel(self):
        if self._call:
            self._call.cancel()

    def __call__(self):
        self._call = None
        return self._func(*self._a, **self._kw)

from twisted.internet import reactor, error

def listen_tcp(portrange, host, factory):
    """Like reactor.listenTCP but tries different ports in a range."""
    assert len(portrange) <= 2, "invalid portrange: %s" % portrange
    if not portrange:
        return reactor.listenTCP(0, factory, interface=host)
    if not hasattr(portrange, '__iter__'):
        return reactor.listenTCP(portrange, factory, interface=host)
    if len(portrange) == 1:
        return reactor.listenTCP(portrange[0], factory, interface=host)
    for x in range(portrange[0], portrange[1]+1):
        try:
            return reactor.listenTCP(x, factory, interface=host)
        except error.CannotListenError:
            if x == portrange[1]:
                raise


class CallLaterOnce(object):
    """Schedule a function to be called in the next reactor loop, but only if
    it hasn't been already scheduled since the last time it ran.
    """

    def __init__(self, func, *a, **kw):
        self._func = func
        self._a = a
        self._kw = kw
        self._call = None

    def schedule(self, delay=0):
        if self._call is None:
            self._call = reactor.callLater(delay, self)

    def cancel(self):
        if self._call:
            self._call.cancel()

    def __call__(self):
        self._call = None
        return self._func(*self._a, **self._kw)

Update reactor.py, updated 'if' sequencing , possibly eliminating a bug if portrange=None