code: def set_reviewing(self, hit_id, revert=None):
          
          params = {'HITId' : hit_id,}
          if revert:
              params['Revert'] = revert
          return self._process_request('SetHITAsReviewing', params)
docs: Update a HIT with a status of Reviewable to have a status of Reviewing, 
          or reverts a Reviewing HIT back to the Reviewable status.
  
          Only HITs with a status of Reviewable can be updated with a status of
          Reviewing.  Similarly, only Reviewing HITs can be reverted back to a
          status of Reviewable.