def RestrictFeedItemToAdGroup(client, feed_item, adgroup_id):
  """Restricts the feed item to an ad group.

  Args:
    client: an AdWordsClient instance.
    feed_item: The feed item.
    adgroup_id: The ad group ID.
  """
  # Get the FeedItemTargetService
  feed_item_target_service = client.GetService(
      'FeedItemTargetService', 'v201809')

  # Optional: Restrict the first feed item to only serve with ads for the
  # specified ad group ID.
  ad_group_target = {
      'xsi_type': 'FeedItemAdGroupTarget',
      'feedId': feed_item['feedId'],
      'feedItemId': feed_item['feedItemId'],
      'adGroupId': adgroup_id
  }

  operation = {'operator': 'ADD', 'operand': ad_group_target}

  response = feed_item_target_service.mutate([operation])
  new_ad_group_target = response['value'][0]

  print('Feed item target for feed ID %s and feed item ID %s was created to '
        'restrict serving to ad group ID %s' %
        (new_ad_group_target['feedId'],
         new_ad_group_target['feedItemId'],
         new_ad_group_target['adGroupId']))