def get_id_lists(zen_tickets, zen_fieldid):
    """Gets lists of the Zendesk user IDs and the GitHub issue numbers that are
    associated with the passed list of Zendesk tickets.

    Parameters:
        zen_tickets - A list of Zendesk tickets whose associated GitHub issue
                    numbers and Zendesk user IDs are desired.
        zen_fieldid - The ID number of the custom field in Zendesk tickets that
                        holds its associated GitHub issue number.

    Returns a tuple of two value with the first being the gathered list of
    associated Zendesk user IDs and with the second being the gathered list
    of associated GitHub issue numbers.
    """

    # Get Zendesk user IDs that are associated with Zendesk tickets.
    zen_user_ids = []
    for ticket in zen_tickets:
        zen_user_ids.append(ticket['requester_id'])
    zen_user_ids = list(set(zen_user_ids)) # Remove duplicates

    # Get GitHub issue numbers that are associated with the Zendesk tickets.
    git_issue_numbers = []
    for ticket in zen_tickets:
        association_data = ''
        for field in ticket['fields']:
            if field['id'] == zen_fieldid:
                if field['value'] is not None:
                    association_data = field['value'].split('-')
                break
        if association_data and association_data[0] == 'gh':
            git_issue_numbers.append(int(association_data[1]))
    git_issue_numbers = list(set(git_issue_numbers)) # Remove duplicates

    return (zen_user_ids, git_issue_numbers)