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()

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()

Add marker to indicate backend error
Add marker to indicate backend error

  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()
  
Add marker to indicate backend error
## Code Before:
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()

## Instruction:
Add marker to indicate backend error
## Code After:
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()
