code: def _get_cbt_binary_path(env_var_name, search_paths, description):
      res = os.environ.get(env_var_name)
      if res is not None:
          if not os.path.isfile(res):
              raise OSError(
                  f"{description} specified in the {env_var_name} "
                  "environment variable does not exist"
              )
          return res
      for candidate in search_paths:
          if os.path.isfile(candidate):
              return candidate
      raise OSError(f"Could not find {description}")
  
file_path: io/tests/test_bigtable/bigtable_emulator.py
imports: import os
  import subprocess
  import re
  import tensorflow
  from threading import Thread
  from typing import List
label_desc: Use image node_id 1 for calling a global function with example usage: _get_cbt_binary_path(env_var_name, search_paths, description) and returns: res, candidate