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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_canonical_block_header_by_number(self, block_number: BlockNumber) -> BlockHeader: """ Returns the block header with the given number in the canonical chain. Raises BlockNotFound if there's no block header with the given number in the canonical chain. """

        return self._get_canonical_block_header_by_number(self.db, block_number)