How to use the asyncssh.public_key.KeyExportError function in asyncssh

:param format_name: (optional)
               The format to export the certificate in.
           :type format_name: `str`

           :returns: `bytes` representing the exported certificate

        """

        if self.is_x509:
            if format_name == 'rfc4716':
                raise KeyExportError('RFC4716 format is not supported for '
                                     'X.509 certificates')
        else:
            if format_name in ('der', 'pem'):
                raise KeyExportError('DER and PEM formats are not supported '
                                     'for OpenSSH certificates')

        if format_name == 'der':
            return self.public_data
        elif format_name == 'pem':
            return (b'-----BEGIN CERTIFICATE-----\n' +
                    _wrap_base64(self.public_data) +
                    b'-----END CERTIFICATE-----\n')
        elif format_name == 'openssh':
            if self._comment:
                comment = b' ' + self._comment
            else:
                comment = b''

            return (self.algorithm + b' ' +
                    binascii.b2a_base64(self.public_data)[:-1] +

def encode_pkcs8_public(self):
        """Export parameters associated with a PKCS#8 public key"""

        # pylint: disable=no-self-use
        raise KeyExportError('PKCS#8 public key export not supported')

def encode_ssh_private(self):
        """Encode an SSH format EC private key"""

        if not self._d:
            raise KeyExportError('Key is not private')

        return b''.join((String(self._alg_id), String(self._Q.encode()),
                         MPInt(self._d)))

der, pem, openssh, rfc4716

           By default, OpenSSH format will be used.

           :param format_name: (optional)
               The format to export the certificate in.
           :type format_name: `str`

           :returns: `bytes` representing the exported certificate

        """

        if self.is_x509:
            if format_name == 'rfc4716':
                raise KeyExportError('RFC4716 format is not supported for '
                                     'X.509 certificates')
        else:
            if format_name in ('der', 'pem'):
                raise KeyExportError('DER and PEM formats are not supported '
                                     'for OpenSSH certificates')

        if format_name == 'der':
            return self.public_data
        elif format_name == 'pem':
            return (b'-----BEGIN CERTIFICATE-----\n' +
                    _wrap_base64(self.public_data) +
                    b'-----END CERTIFICATE-----\n')
        elif format_name == 'openssh':
            if self._comment:
                comment = b' ' + self._comment
            else:

def encode_pkcs1_private(self):
        """Export parameters associated with a PKCS#1 private key"""

        # pylint: disable=no-self-use
        raise KeyExportError('PKCS#1 private key export not supported')

def encode_ssh_private(self):
        """Encode an SSH format Ed25519 private key"""

        if self._sk is None:
            raise KeyExportError('Key is not private')

        return b''.join((String(self._vk), String(self._sk)))

def encode_pkcs8_private(self):
        """Export parameters associated with a PKCS#8 private key"""

        # pylint: disable=no-self-use
        raise KeyExportError('PKCS#8 private key export not supported')

data = data + bytes(range(1, block_size + 1 - pad))

            if cipher:
                data, mac = cipher.encrypt_packet(0, b'', data)
            else:
                mac = b''

            data = b''.join((_OPENSSH_KEY_V1, String(alg), String(kdf),
                             String(kdf_data), UInt32(nkeys),
                             String(self.public_data), String(data), mac))

            return (b'-----BEGIN OPENSSH PRIVATE KEY-----\n' +
                    _wrap_base64(data, _OPENSSH_WRAP_LEN) +
                    b'-----END OPENSSH PRIVATE KEY-----\n')
        else:
            raise KeyExportError('Unknown export format')