code: def import_header(self,
                        header: BlockHeader
                        ) -> Tuple[Tuple[BlockHeader, ...], Tuple[BlockHeader, ...]]:
          
          new_canonical_headers = self.headerdb.persist_header(header)
          self.header = self.get_canonical_head()
          return new_canonical_headers
docs: Direct passthrough to `headerdb`
  
          Also updates the local `header` property to be the latest canonical head.
  
          Returns an iterable of headers representing the headers that are newly
          part of the canonical chain.
  
          - If the imported header is not part of the canonical chain then an
            empty tuple will be returned.
          - If the imported header simply extends the canonical chain then a
            length-1 tuple with the imported header will be returned.
          - If the header is part of a non-canonical chain which overtakes the
            current canonical chain then the returned tuple will contain the
            headers which are newly part of the canonical chain.