def GetCustomerIDs(client):
  """Retrieves all CustomerIds in the account hierarchy.

  Note that your configuration file must specify a client_customer_id belonging
  to an AdWords manager account.

  Args:
    client: an AdWordsClient instance.
  Raises:
    Exception: if no CustomerIds could be found.
  Returns:
    A Queue instance containing all CustomerIds in the account hierarchy.
  """
  # For this example, we will use ManagedCustomerService to get all IDs in
  # hierarchy that do not belong to MCC accounts.
  managed_customer_service = client.GetService('ManagedCustomerService',
                                               version='v201809')

  offset = 0

  # Get the account hierarchy for this account.
  selector = {
      'fields': ['CustomerId'],
      'predicates': [{
          'field': 'CanManageClients',
          'operator': 'EQUALS',
          'values': [False]
      }],
      'paging': {
          'startIndex': str(offset),
          'numberResults': str(PAGE_SIZE)
      }
  }

  # Using Queue to balance load between processes.
  queue = multiprocessing.Queue()
  more_pages = True

  while more_pages:
    page = managed_customer_service.get(selector)

    if page and 'entries' in page and page['entries']:
      for entry in page['entries']:
        queue.put(entry['customerId'])
    else:
      raise Exception('Can\'t retrieve any customer ID.')
    offset += PAGE_SIZE
    selector['paging']['startIndex'] = str(offset)
    more_pages = offset < int(page['totalNumEntries'])

  return queue