code: def preorder_traversal(task):
      """A generator to preorder-traverse a task."""
  
      for item in task:
          if istask(item):
              yield from preorder_traversal(item)
          elif isinstance(item, list):
              yield list
              yield from preorder_traversal(item)
          else:
              yield item
  
imports: from collections import defaultdict
  from typing import List, Sequence
  from flash.core.utilities.imports import _TOPIC_SERVE_AVAILABLE
label_desc: Use image node_id 3 for calling a global function with example usage: preorder_traversal(task) without return types