old_contents: class InvalidDefinitionError(Exception):
      pass
  
  
  class NotFoundError(Exception):
      pass
  
  
  class ProcessingError(Exception):
      '''
      An error occurred while processing a request to the XModule.
      For example: if an exception occurs while checking a capa problem.
      '''
      pass
  
  
  class InvalidVersionError(Exception):
      """
      Tried to save an item with a location that a store cannot support (e.g., draft version
      for a non-leaf node)
      """
      def __init__(self, location):
          super(InvalidVersionError, self).__init__()
          self.location = location
  
  
  class SerializationError(Exception):
      """
      Thrown when a module cannot be exported to XML
      """
      def __init__(self, location, msg):
          super(SerializationError, self).__init__(msg)
          self.location = location
  
  
  class UndefinedContext(Exception):
      """
      Tried to access an xmodule field which needs a different context (runtime) to have a value.
      """
      pass
  
  
  class HeartbeatFailure(Exception):
      """
      Raised when heartbeat fails.
      """
  
      def __unicode__(self, *args, **kwargs):
          return self.message
  
      def __init__(self, msg, service):
          """
          In addition to a msg, provide the name of the service.
          """
          self.service = service
          return super(HeartbeatFailure, self).__init__(msg)
  
new_contents: class InvalidDefinitionError(Exception):
      pass
  
  
  class NotFoundError(Exception):
      pass
  
  
  class ProcessingError(Exception):
      '''
      An error occurred while processing a request to the XModule.
      For example: if an exception occurs while checking a capa problem.
      '''
      pass
  
  
  class InvalidVersionError(Exception):
      """
      Tried to save an item with a location that a store cannot support (e.g., draft version
      for a non-leaf node)
      """
      def __init__(self, location):
          super(InvalidVersionError, self).__init__()
          self.location = location
  
  
  class SerializationError(Exception):
      """
      Thrown when a module cannot be exported to XML
      """
      def __init__(self, location, msg):
          super(SerializationError, self).__init__(msg)
          self.location = location
  
  
  class UndefinedContext(Exception):
      """
      Tried to access an xmodule field which needs a different context (runtime) to have a value.
      """
      pass
  
  
  class HeartbeatFailure(Exception):
      """
      Raised when heartbeat fails.
      """
  
      def __unicode__(self, *args, **kwargs):
          return self.message
  
      def __init__(self, msg, service):
          """
          In addition to a msg, provide the name of the service.
          """
          self.service = service
          super(HeartbeatFailure, self).__init__(msg)
  
subject: Fix Pylint: E0101(return-in-init)