old_contents: """
  Simple runner for `ipcluster start` or `ipcluster stop` on Python 2 or 3, as
  appropriate.
  """
  
  import sys
  import six
  from subprocess import Popen, PIPE
  
  
  if six.PY2:
      ipcluster_cmd = 'ipcluster'
  elif six.PY3:
      ipcluster_cmd = 'ipcluster3'
  else:
      raise NotImplementedError("Not run with Python 2 *or* 3?")
  
  
  def start(n=12):
      """Convenient way to start an ipcluster for testing.
  
      You have to wait for it to start, however.
      """
      # FIXME: This should be reimplemented to signal when the cluster has
      # successfully started
  
      engines = "--engines=MPIEngineSetLauncher"
      Popen([ipcluster_cmd, 'start', '-n', str(n), engines, str('&')],
             stdout=PIPE, stderr=PIPE)
  
  
  def stop():
      """Convenient way to stop an ipcluster."""
  
      Popen([ipcluster_cmd, 'stop'], stdout=PIPE, stderr=PIPE)
  
  
  if __name__ == '__main__':
      cmd = sys.argv[1]
      fn = eval(cmd)
      fn()
  
new_contents: """
  Simple runner for `ipcluster start` or `ipcluster stop` on Python 2 or 3, as
  appropriate.
  """
  
  import sys
  import six
  from subprocess import Popen, PIPE
  
  
  if six.PY2:
      ipcluster_cmd = 'ipcluster'
  elif six.PY3:
      ipcluster_cmd = 'ipcluster3'
  else:
      raise NotImplementedError("Not run with Python 2 *or* 3?")
  
  
  def start(n=4):
      """Convenient way to start an ipcluster for testing.
  
      You have to wait for it to start, however.
      """
      # FIXME: This should be reimplemented to signal when the cluster has
      # successfully started
  
      engines = "--engines=MPIEngineSetLauncher"
      Popen([ipcluster_cmd, 'start', '-n', str(n), engines, str('&')],
             stdout=PIPE, stderr=PIPE)
  
  
  def stop():
      """Convenient way to stop an ipcluster."""
  
      Popen([ipcluster_cmd, 'stop'], stdout=PIPE, stderr=PIPE)
  
  
  if __name__ == '__main__':
      cmd = sys.argv[1]
      fn = eval(cmd)
      fn()
  
subject: Change the default number of engines to 4.