code: def _update_key(self):
      values = []
      for value in self._values_:
          if isinstance(value, self._tree_type):
              values.append(cloudpickle.dumps(value))
          else:
              values.append(value)
      self._obj_set("_key", tokenize(type(self).__name__, *values))
      return self
  
imports: import cloudpickle
  import numpy
  from ...core import Object, OBJECT_TYPE, OBJECT_CHUNK_TYPE, recursive_tile
  from ...serialization.serializables import KeyField, Int32Field, DictField, AnyField, BoolField
  from ...tensor.core import TensorOrder
  from ...utils import has_unknown_shape, tokenize
  from ..operands import LearnOperand, LearnOperandMixin, OutputType
label_desc: Use image node_id 8 for calling the TreeQueryBase obj's underlying member method code with example usage: obj._update_key() and returns: self