code: def check( state_engine, nameop, block_id, checked_ops ):
      
  
      sender = nameop['sender']
      sending_blockchain_id = None
      found = False
      blockchain_namerec = None
  
      for blockchain_id in state_engine.get_announce_ids():
          blockchain_namerec = state_engine.get_name( blockchain_id )
          if blockchain_namerec is None:
              # this name doesn't exist yet, or is expired or revoked
              continue
  
          if str(sender) == str(blockchain_namerec['sender']):
              # yup!
              found = True
              sending_blockchain_id = blockchain_id
              break
  
      if not found:
          log.warning("Announcement not sent from our whitelist of blockchain IDs")
          return False
  
      nameop['announcer_id'] = sending_blockchain_id
      process_announcement( blockchain_namerec, nameop, state_engine.working_dir )
      return True
docs: Log an announcement from the blockstack developers,
      but first verify that it is correct.
      Return True if the announcement came from the announce IDs whitelist
      Return False otherwise