new_contents: __author__ = 'mengpeng'
  
  
  class PyCrawlerException(Exception):
      pass
  
  
  class ScraperException(PyCrawlerException):
      pass
  
  
  class HandlerException(PyCrawlerException):
      pass
  
  
  class FrontierException(PyCrawlerException):
      pass
  
  
  class PersistException(PyCrawlerException):
      pass
subject: add exception.py