def mime_type(filename):
    return guess_type(filename)[0]


class ServeSavedDocument(blobstore_handlers.BlobstoreDownloadHandler):

    def get(self):
        blob_key = self.request.get('blob_key')
if blob_key:
    blob_info = blobstore.get(blob_key)
if blob_info:
    save_as1 = blob_info.filename
type1 = mime_type(blob_info.filename)
self.send_blob(blob_info, content_type=type1, save_as=save_as1)
How can I retrieve a file object from the blobstore within a handler?