How to set region with Python boto AWS

I am trying to access my AWS buckets with Python boto.

I can access buckets with the region US Standard.

import boto
c = boto.connect_s3()
print c.lookup('boto-test-us-standard')

However if I try to access a bucket with a different region, it doesn't find the bucket.

print c.lookup('boto-test-frankfurt')

Where can I set the region boto uses?