code: def sign_bitcoin(self, message, compressed=False):
          
  
          return self._key.sign_bitcoin(message, compressed)
docs: Signs a message using the underlying non-extended private
          key such that it is compatible with bitcoind, bx, and other
          Bitcoin clients/nodes/utilities.
  
          Note:
              0x18 + b\"Bitcoin Signed Message:" + newline + len(message) is
              prepended to the message before signing.
  
          Args:
              message (bytes or str): Message to be signed.
              compressed (bool):
                  True if the corresponding public key will be
                  used in compressed format. False if the uncompressed version
                  is used.
  
          Returns:
              bytes: A Base64-encoded byte string of the signed message.
              The first byte of the encoded message contains information
              about how to recover the public key. In bitcoind parlance,
              this is the magic number containing the recovery ID and
              whether or not the key was compressed or not. (This function
              always processes full, uncompressed public-keys, so the
              magic number will always be either 27 or 28).