def generate_scope_string(date, region, service_name):
    """
    Generate scope string.

    :param date: Date is input from :meth:`datetime.datetime`
    :param region: Region should be set to bucket region.
    :param service_name: Service for scope string, e.g., "s3".
    """
    formatted_date = date.strftime('%Y%m%d')
    scope = '/'.join([formatted_date, region, service_name, 'aws4_request'])
    return scope
