text: class BaseApostleError(Exception):
      """
      Base class for all Apostle errors.
      """
  
      def __init__(self, message):
          super(BaseApostleError, self).__init__()
          self._message = message
  
      def __str__(self):
          # all sub-classes should set self._message in their initializers
          return self._message
  
  
  class DeliveryError(BaseApostleError): pass
  class UnauthorizedError(BaseApostleError): pass
  class ForbiddenError(BaseApostleError): pass
  class ServerError(BaseApostleError): pass
  class UnprocessableEntityError(BaseApostleError): pass
  class ValidationError(BaseApostleError): pass
  