old_contents: def printerr(msg, e=''):
      print(msg.format(e), file=sys.stderr)
  
  class CommunicationError(Exception):
      def __str__(self):
          return "Communication error: {}".format(self.args)
  
  class CommandError(Exception):
      def __str__(self):
          return "Command error: {}".format(self.args)
  
  class Syringe():
      _events = set()
  
      def __init__(self):
          pass
  
      def execRawCommand(self, msg):
          """
          Send command and read reply.
          """
          pass
  
      # Read Perfusion related values
      def readRate(self):
          return 0
  
      def readVolume(self):
          return 0
  
      # Infusion control
      def setRate(self, rate):
          pass
  
      def bolus(self, volume, rate):
          pass
  
      # Events
      def registerEvent(self, event):
          self._events |= set([event])
  
      def unregisterEvent(self, event):
          self._events -= set([event])
  
      def clearEvents(self):
          self._events = set()
  
new_contents: def printerr(msg, e=''):
      msg = "Backend: " + str(msg)
      print(msg.format(e), file=sys.stderr)
  
  class CommunicationError(Exception):
      def __str__(self):
          return "Communication error: {}".format(self.args)
  
  class CommandError(Exception):
      def __str__(self):
          return "Command error: {}".format(self.args)
  
  class Syringe():
      _events = set()
  
      def __init__(self):
          pass
  
      def execRawCommand(self, msg):
          """
          Send command and read reply.
          """
          pass
  
      # Read Perfusion related values
      def readRate(self):
          return 0
  
      def readVolume(self):
          return 0
  
      # Infusion control
      def setRate(self, rate):
          pass
  
      def bolus(self, volume, rate):
          pass
  
      # Events
      def registerEvent(self, event):
          self._events |= set([event])
  
      def unregisterEvent(self, event):
          self._events -= set([event])
  
      def clearEvents(self):
          self._events = set()
  
subject: Add marker to indicate backend error