code: def walk_files(directory):
      for root, _, files in os.walk(directory):
          for f in files:
              yield os.path.join(root, f)
  
imports: import logging
  import os
  import shutil
  import stat
  import textwrap
  import pytest
  from dvc.cli import main
  from dvc.dvcfile import PROJECT_FILE, load_file
  from dvc.exceptions import CheckoutError, CheckoutErrorSuggestGit, NoOutputOrStageError
  from dvc.fs import system
  from dvc.stage.exceptions import StageFileDoesNotExistError
  from dvc.utils import relpath
  from dvc.utils.fs import remove
  from tests.utils import get_gitignore_content
label_desc: Use image node_id 1 for calling a global function with example usage: walk_files(directory) without return types