code: def get_base_dir(base_dir):
      return (
          base_dir
          if not "CNTK_EXTERNAL_TESTDATA_SOURCE_DIRECTORY" in os.environ
          else os.path.join(
              os.environ["CNTK_EXTERNAL_TESTDATA_SOURCE_DIRECTORY"],
              base_dir,
          )
      )
  
file_path: CNTK/bindings/python/cntk/tests/onnx_model_test.py
imports: import cntk
  import numpy
  import pytest
  import os
  import re
  import shutil
  import time
  import tempfile
  from onnx import numpy_helper
  from .onnx_verify_helper import generate_sequence_data, generate_sequential_data, generate_sparse_data, verify_results_with_onnxruntime, generate_sparse_data_non_seq
  from .onnx_test_helper import find_onnx_value_info_proto_with_matching_name, save_cntk_data_as_onnx_tensor, save_test_data, save_onnx_model_with_validation_data
  from .onnx_op_test import verify_sequence_model
label_desc: Use image node_id 1 for calling a global function with example usage: get_base_dir(base_dir) and returns: unknown