code: def test_artifact_bracket_accessor(user, api, sample_data):
      art = api.artifact("mnist:v1", type="dataset")
      assert art["t"].__class__ == wandb.Table
      assert art["s"] is None
      with pytest.raises(ArtifactFinalizedError):
          art["s"] = wandb.Table(data=[], columns=[])
  
imports: import os
  import platform
  import pytest
  import wandb
  from wandb.sdk.artifacts.exceptions import ArtifactFinalizedError
label_desc: Use image node_id 16 for calling a global function with example usage: test_artifact_bracket_accessor(user, api, sample_data) without return types