Is it possible to use the S3 multipart upload with strings instead of a file? The strings i am using are being generated during the upload process and so the size and the exact content is unknown the time the multipart upload starts.
There is no explicit "upload_part_from_string" method available.  You could probably use StringIO to wrap a file-like object around the string and then pass that to "upload_part_from_file" but I haven't tested that.
It would be easy to add this method.  At the time I didn't think it would be all that useful since each of the parts has to be a minimum of 5MB and that's a pretty big string.  But if you have a use case for it, let me know.  Or, fork boto on github, add the method and send a pull request.
Can you use multipart upload in boto with strings instead of a file handler?