code: def walk_tree(
      root,
      *,
      suffix=None,
      walk=_walk_tree,
  ):
      """Yield each file in the tree under the given directory name.
  
      If "suffix" is provided then only files with that suffix will
      be included.
      """
      if suffix and not isinstance(suffix, str):
          raise ValueError("suffix must be a string")
  
      for filename in walk(root):
          if suffix and not filename.endswith(suffix):
              continue
          yield filename
  
imports: import fnmatch
  import glob
  import os
  import os.path
  import shutil
  import stat
  from .iterutil import iter_many
label_desc: Use image node_id 14 for calling a global function with example usage: walk_tree(root) without return types