code: def get_valid_consensus_hashes( self, block_id ):
          
          first_block_to_check = block_id - self.impl.get_valid_transaction_window()
  
          query = 'SELECT consensus_hash FROM snapshots WHERE block_id >= ? AND block_id <= ?;'
          args = (first_block_to_check,block_id)
  
          valid_consensus_hashes = []
          
          con = self.db_open(self.impl, self.working_dir)
          rows = self.db_query_execute(con, query, args, verbose=False)
  
          for r in rows:
              assert r['consensus_hash'] is not None
              assert isinstance(r['consensus_hash'], (str,unicode))
  
              valid_consensus_hashes.append(str(r['consensus_hash']))
  
          con.close()
          return valid_consensus_hashes
docs: Get the list of valid consensus hashes for a given block.