code: def valid_regions(zone: Optional[str] = None) -> List[Region]:
      """Returns valid region strings for Cloud, for the globe or for a particular
      region if specified.
  
      """
      if zone is None:
          return (
              valid_regions("americas")
              + valid_regions("europe")
              + valid_regions("asia")
          )
      z = zone.lower()
      if z == "americas":
          return list(US) + list(NorthAmerica) + list(SouthAmerica)
      elif z == "europe":
          return list(Europe)
      elif z == "asia":
          return list(Asia) + list(Australia)
      else:
          raise ValueError(
              "invalid zone: {}. Must be one of 'americas', 'europe', 'asia'.".format(
                  zone
              )
          )
  
imports: import argparse
  from enum import Enum
  from typing import Callable, List, NamedTuple, Optional, Set, Union
  import caliban.util
label_desc: Use image node_id 2 for calling a global function with example usage: valid_regions(zone) and returns: unknown, unknown, list, unknown