python - 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 off the "Content-length" header of a "HEAD" request. But I'm not connecting the dots about how to do this with boto. Extra kudos if you post a link to some more comprehensive examples than are in the standard boto docs.

EDIT: So the following seems to do the trick (though from looking at source code I'm not completely sure.):

bk = conn.get_bucket('my_bucket_name')
ky = boto.s3.key.Key(bk)
ky.open_read()  ## This sends a GET request. 
print ky.size

For now I'll leave the question open for comments, better solutions, or pointers to examples.

Answer 1

This would work:

bk = conn.get_bucket('my_bucket_name')
key = bk.lookup('my_key_name')
print key.size

The lookup method simply does a HEAD request on the bucket for the keyname so it will return all of the headers (including content-length) for the key but will not transfer any of the actual content of the key.

The S3 tutorial mentions this but not very explicitly and not in this exact context. I'll add a section on this to help make it easier to find.

Note: for every old link like http://boto.cloudhackers.com/s3_tut.html that returns a 404, add in "/en/latest" right after the ".com" : http://boto.cloudhackers.com/en/latest/s3_tut.html . (Someone needs to explore mod_rewrite...)