async def load_artifact(
      self, filename: str, version: Optional[int] = None
  ) -> Optional[types.Part]:
    """Loads an artifact attached to the current session.

    Args:
      filename: The filename of the artifact.
      version: The version of the artifact. If None, the latest version will be
        returned.

    Returns:
      The artifact.
    """
    if self._invocation_context.artifact_service is None:
      raise ValueError("Artifact service is not initialized.")
    return await self._invocation_context.artifact_service.load_artifact(
        app_name=self._invocation_context.app_name,
        user_id=self._invocation_context.user_id,
        session_id=self._invocation_context.session.id,
        filename=filename,
        version=version,
    )
Loads an artifact attached to the current session.

    Args:
      filename: The filename of the artifact.
      version: The version of the artifact. If None, the latest version will be
        returned.

    Returns:
      The artifact.
    
src/google/adk/agents/callback_context.py