code: def _AddCampaignsToGroup(client, campaign_group_id, campaign_ids):
    
    # Get the CampaignService.
    campaign_service = client.GetService('CampaignService', version='v201809')
  
    # Create the operations.
    operations = [{
        'operator': 'SET',
        'operand': {
            'id': campaign_id,
            'campaignGroupId': campaign_group_id
        }
    } for campaign_id in campaign_ids]
  
    campaign_service.mutate(operations)
  
    # Display the results.
    print ('The following campaign IDs were added to the campaign group with ID '
           '"%d":\n\t%s' % (campaign_group_id, campaign_ids))
docs: Adds multiple campaigns to a campaign group.
  
    Args:
      client: an AdWordsClient instance.
      campaign_group_id: an integer ID for the campaign group.
      campaign_ids: a list of integer IDs for campaigns.