code: def start(cmd, port=None, numRetries=10, label="default"):
      
      if port is None:
          port = sumolib.miscutils.getFreeSocketPort()
      sumoProcess = subprocess.Popen(cmd + ["--remote-port", str(port)])
      _connections[label] = connect(port, numRetries, "localhost", sumoProcess)
      switch(label)
      return getVersion()
docs: Start a sumo server using cmd, establish a connection to it and
      store it under the given label. This method is not thread-safe.