code: def get_all_ad_units(inventory_service):
    
    # Create a statement to get all ad units.
    statement = (ad_manager.StatementBuilder(version='v201811')
                 .OrderBy('id', ascending=True))
  
    # Pull down all ad units into a list
    keep_iterating = True
    total_results = 0
    found_ad_units = []
    while keep_iterating:
      page = inventory_service.getAdUnitsByStatement(statement.ToStatement())
      if 'results' in page and len(page['results']):
        total_results = page['totalResultSetSize']
        found_ad_units.extend(page['results'])
  
      statement.offset += statement.limit
      keep_iterating = statement.offset < total_results
  
    return found_ad_units
docs: Download all ad units.
  
    Args:
      inventory_service: An instance of the InventoryService.
  
    Returns:
      A list containing all ad units.