I have my $AWS_ACCESS_KEY_ID and $AWS_SECRET_ACCESS_KEY environment variables set properly, and I run this code:
import boto conn = boto.connect_s3()
You can now set these as arguments in the connect function call.
s3 = boto.connect_s3(AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY)
Just thought I'd add that incase anyone else searched like I did.