text: from typing import Type
  
  from lib.vsm import VSM
  
  
  class InvalidTransitionError(Exception):
      def __init__(self, current_state: Type[VSM], next_state: Type[VSM]):
          self.start = current_state
          self.end = next_state
          message = "An invalid transition was attempted: {} --> {}"\
                    .format(self.start, self.end)
          super().__init__(message)
  