Can you upload to S3 using a stream rather than a local file?

I need to create a CSV and upload it to an S3 bucket. Since I'm creating the file on the fly, it would be better if I could write it directly to S3 bucket as it is being created rather than writing the whole file locally, and then uploading the file at the end.

Is there a way to do this? My project is in Python and I'm fairly new to the language. Here is what I tried so far:

import csv
import csv
import io
import boto
from boto.s3.key import Key


conn = boto.connect_s3()
bucket = conn.get_bucket('dev-vs')
k = Key(bucket)
k.key = 'foo/foobar'

fieldnames = ['first_name', 'last_name']
writer = csv.DictWriter(io.StringIO(), fieldnames=fieldnames)
k.set_contents_from_stream(writer.writeheader())