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 __future__ import annotations
  from collections import defaultdict
  from collections.abc import Collection, Iterable, Mapping
  from typing import Any, Literal, TypeVar, cast, overload
  from dask.typing import Graph, Key, NoDefault, no_default
label_desc: Use image node_id 4 for calling a global function with example usage: preorder_traversal(task) without return types