s3 = boto3.session.Session(profile_name=my_profile).resource('s3')
s3_obj = s3.Object(bucket_name=my_bucket, key=my_key)
with io.FileIO('sample.txt', 'w') as file:
    for i in s3_obj:
        file.write(i)
How can I use boto to stream a file out of Amazon S3 to Rackspace Cloudfiles?