Streaming tornado uploads to Amazon S3

Handler.py

@web.stream_request_body
class UploadHandler(RequestHandler):

    def prepare(self):
        self.count = 0
        self.buffer_len = 0
        self.buffer = StringIO()
        self.mp = bucket.initiate_multipart_upload('Multiparts are cool')

    def data_received(self, data):
        self.buffer.write(data)
        self.buffer_len+=len(data)

        if self.buffer_len >= 5 * 1024**2:
            self.flush_buffer()

    def flush_buffer(self):
        self.buffer.seek(0)
        self.count += 1
        self.mp.upload_part_from_file(self.buffer, self.count)
        self.buffer = StringIO()
        self.buffer_len = 0

    def post(self):
        if self.count == 0:
            self.buffer.seek(0)
            key = bucket.new_key('Singles are cool too')
            key.set_contents_from_file(self.buffer)
        else:
            if self.buffer_len != 0:
                self.flush_buffer()
            complete = self.mp.complete_upload()