old_contents: 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 run.
      """
  
      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)
  
new_contents: 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)
  
subject: Fix typo in docstring