code: def get_crawl_delay(self, user_agent):
          
          # See is_allowed() comment about the explicit unicode conversion.
          if (PY_MAJOR_VERSION < 3) and (not isinstance(user_agent, unicode)):
              user_agent = user_agent.decode()
      
          for ruleset in self.__rulesets:
              if ruleset.does_user_agent_match(user_agent):
                  return ruleset.crawl_delay
                  
          return None
docs: Returns a float representing the crawl delay specified for this 
          user agent, or None if the crawl delay was unspecified or not a float.