How to use the tink.proto.tink_pb2 function in tink

def write(self, keyset: tink_pb2.Keyset) -> None:
    if not isinstance(keyset, tink_pb2.Keyset):
      raise tink_error.TinkError('invalid keyset.')
    json_keyset = json_format.MessageToJson(keyset)
    # TODO(b/141106504) Needed for python 2.7 compatibility. StringIO expects
    # unicode, but MessageToJson outputs UTF-8.
    if isinstance(json_keyset, bytes):
      json_keyset = json_keyset.decode('utf-8')
    self._io_stream.write(json_keyset)
    self._io_stream.flush()

def _validate_keyset(keyset: tink_pb2.Keyset):
  """Raises tink_error.TinkError if keyset is not valid."""
  for key in keyset.key:
    if key.status != tink_pb2.DESTROYED:
      _validate_key(key)
  num_non_destroyed_keys = sum(
      1 for key in keyset.key if key.status != tink_pb2.DESTROYED)
  num_non_public_key_material = sum(
      1 for key in keyset.key
      if key.key_data.key_material_type != tink_pb2.KeyData.ASYMMETRIC_PUBLIC)
  num_primary_keys = sum(
      1 for key in keyset.key
      if key.status == tink_pb2.ENABLED and key.key_id == keyset.primary_key_id)
  if num_non_destroyed_keys == 0:
    raise tink_error.TinkError('empty keyset')
  if num_primary_keys > 1:
    raise tink_error.TinkError('keyset contains multiple primary keys')
  if num_primary_keys == 0 and num_non_public_key_material > 0:
    raise tink_error.TinkError('keyset does not contain a valid primary key')

def write_encrypted(self, encrypted_keyset: tink_pb2.EncryptedKeyset) -> None:
    if not isinstance(encrypted_keyset, tink_pb2.EncryptedKeyset):
      raise tink_error.TinkError('invalid encrypted keyset.')
    json_keyset = json_format.MessageToJson(encrypted_keyset)
    # TODO(b/141106504) Needed for python 2.7 compatibility. StringIO expects
    # unicode, but MessageToJson outputs UTF-8.
    if isinstance(json_keyset, bytes):
      json_keyset = json_keyset.decode('utf-8')
    self._io_stream.write(json_keyset)
    self._io_stream.flush()

def _validate_key(key: tink_pb2.Keyset.Key):
  """Raises tink_error.TinkError if key is not valid."""
  if not key.HasField('key_data'):
    raise tink_error.TinkError('key {} has no key data'.format(key.key_id))
  if key.output_prefix_type == tink_pb2.UNKNOWN_PREFIX:
    raise tink_error.TinkError('key {} has unknown prefix'.format(key.key_id))
  if key.status == tink_pb2.UNKNOWN_STATUS:
    raise tink_error.TinkError('key {} has unknown status'.format(key.key_id))