How do I get the file / key size in boto S3?

Question

There must be an easy way to get the file size (key size) without pulling over a whole file. I can see it in the Properties of the AWS S3 browser. And I think I can get it

Answer 1

in boto3:

s3.head_object also performs a HEAD request to retrieve the meta data about the object:

s3 = boto3.client('s3')
response = s3.head_object(Bucket='bucketname', Key='keyname')
size = response['ContentLength']