class_docstr: Utility to find and replace the `source_type` in Python objects.
  
  `source_type` can either be a single type or a tuple of multiple types.
  
  The caller must first call `find_nodes()`, then compute a replacement table and
  pass it to `replace_nodes`.
  
  This uses cloudpickle under the hood, so all sub-objects that are not `source_type`
  must be serializable.
  
  Args:
      source_type: the type(s) of object to find and replace. Default to DAGNodeBase.
docstr: Clear the scanner from the _instances
docstr_tok: ["Clear","the","scanner","from","the","_instances"]
code: def clear(self):
      """Clear the scanner from the _instances"""
      if id(self) in _instances:
          del _instances[id(self)]
  
file_path: ray/python/ray/dag/py_obj_scanner.py
imports: import io
  from typing import Any, Dict, Generic, List, Tuple, Type, TypeVar, Union
  import pickle
  import ray
  from ray.dag.base import DAGNodeBase
label_desc: Use image node_id 6 for calling the _PyObjScanner obj's underlying member method code with example usage: obj.clear() without return types