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

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 public_key_data(cls,
                      private_key_data: tink_pb2.KeyData) -> tink_pb2.KeyData:
    """Generates a new key for the specified key_template."""
    if (private_key_data.key_material_type !=
        tink_pb2.KeyData.ASYMMETRIC_PRIVATE):
      raise tink_error.TinkError('The keyset contains a non-private key')
    key_mgr = cls.key_manager(private_key_data.type_url)
    if not isinstance(key_mgr, km_module.PrivateKeyManager):
      raise tink_error.TinkError(
          'manager for key type {} is not a PrivateKeyManager'
          .format(private_key_data.type_url))
    return key_mgr.public_key_data(private_key_data)

def _assert_no_secret_key_material(keyset: tink_pb2.Keyset):
  for key in keyset.key:
    if key.key_data.key_material_type in (tink_pb2.KeyData.UNKNOWN_KEYMATERIAL,
                                          tink_pb2.KeyData.SYMMETRIC,
                                          tink_pb2.KeyData.ASYMMETRIC_PRIVATE):
      raise tink_error.TinkError('keyset contains secret key material')

def _assert_no_secret_key_material(keyset: tink_pb2.Keyset):
  for key in keyset.key:
    if key.key_data.key_material_type in (tink_pb2.KeyData.UNKNOWN_KEYMATERIAL,
                                          tink_pb2.KeyData.SYMMETRIC,
                                          tink_pb2.KeyData.ASYMMETRIC_PRIVATE):
      raise tink_error.TinkError('keyset contains secret key material')

def _assert_no_secret_key_material(keyset: tink_pb2.Keyset):
  for key in keyset.key:
    if key.key_data.key_material_type in (tink_pb2.KeyData.UNKNOWN_KEYMATERIAL,
                                          tink_pb2.KeyData.SYMMETRIC,
                                          tink_pb2.KeyData.ASYMMETRIC_PRIVATE):
      raise tink_error.TinkError('keyset contains secret key material')