code: def open_reader(self, artifact_id: str) -> BinaryIO:
      with self._lock:
          data = self._data.get(artifact_id)
          if data is None:
              raise ArtifactNotFound("not found")
          return copy.deepcopy(data)
  
file_path: optuna/tests/artifacts_tests/stubs.py
imports: from __future__ import annotations
  import copy
  import io
  import shutil
  import threading
  from typing import TYPE_CHECKING
  from optuna.artifacts.exceptions import ArtifactNotFound
label_desc: Use image node_id 2 for calling the InMemoryArtifactStore obj's underlying member method code with example usage: obj.open_reader(artifact_id) and returns: copy