def generate_arn(service, arn_suffix, region=None):
    """Returns a formatted arn for AWS.

    Keyword arguments:
        service -- the AWS service
        arn_suffix -- the majority of the arn after the initial common data
        region -- the region (can be None for region free arns)
    """
    arn_value = "arn"
    aws_value = "aws"
    region_qualified = region if region else ""

    return f"{arn_value}:{aws_value}:{service}:{region_qualified}:{arn_suffix}"