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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_confirmed_blockhash(self):
 """ Gets the block CONFIRMATION_BLOCKS in the past and returns its block hash """

        confirmed_block_number = self.web3.eth.blockNumber - self.default_block_num_confirmations
        if confirmed_block_number < 0:
            confirmed_block_number = 0

        return self.blockhash_from_blocknumber(confirmed_block_number)