code: def import_block(self,
                       block: BaseBlock,
                       perform_validation: bool=True
                       ) -> Tuple[BaseBlock, Tuple[BaseBlock, ...], Tuple[BaseBlock, ...]]:
          
  
          try:
              parent_header = self.get_block_header_by_hash(block.header.parent_hash)
          except HeaderNotFound:
              raise ValidationError(
                  "Attempt to import block #{}.  Cannot import block {} before importing "
                  "its parent block at {}".format(
                      block.number,
                      block.hash,
                      block.header.parent_hash,
                  )
              )
  
          base_header_for_import = self.create_header_from_parent(parent_header)
          imported_block = self.get_vm(base_header_for_import).import_block(block)
  
          # Validate the imported block.
          if perform_validation:
              validate_imported_block_unchanged(imported_block, block)
              self.validate_block(imported_block)
  
          (
              new_canonical_hashes,
              old_canonical_hashes,
          ) = self.chaindb.persist_block(imported_block)
  
          self.logger.debug(
              'IMPORTED_BLOCK: number %s | hash %s',
              imported_block.number,
              encode_hex(imported_block.hash),
          )
  
          new_canonical_blocks = tuple(
              self.get_block_by_hash(header_hash)
              for header_hash
              in new_canonical_hashes
          )
          old_canonical_blocks = tuple(
              self.get_block_by_hash(header_hash)
              for header_hash
              in old_canonical_hashes
          )
  
          return imported_block, new_canonical_blocks, old_canonical_blocks
docs: Imports a complete block and returns a 3-tuple
  
          - the imported block
          - a tuple of blocks which are now part of the canonical chain.
          - a tuple of blocks which were canonical and now are no longer canonical.