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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 sign_transaction(self, signer: Account):
 """ This interface is used to sign the transaction. :param signer: an Account object which will sign the transaction. :return: a Transaction object which has been signed. """

        tx_hash = self.hash256()
        sig_data = signer.generate_signature(tx_hash)
        sig = [Sig([signer.get_public_key_bytes()], 1, [sig_data])]
        self.sig_list = sig