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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 finalize(self):
 """ Get the base64-encoded signature itself. Can only be called once. """

        signature = self.signer.finalize()
        sig_r, sig_s = decode_dss_signature(signature)
        sig_b64 = encode_signature(sig_r, sig_s)
        return sig_b64