code: def errReceived(self, data):
          
  
          if self.stderr:
              self.stderr.write(data)
  
          if self.kill_on_stderr:
              self.transport.loseConnection()
              raise RuntimeError(
                  "Received stderr output from slave Tor process: " + data.decode('utf8')
              )
docs: :api:`twisted.internet.protocol.ProcessProtocol <ProcessProtocol>` API