blobstore tornado uploadhandler config

blobstore_tornado.py

### app.yaml ###
- url: /upload
  script: main.py
  login: admin


### views.py ###
class BlobstoreUpload(BaseHandler):
    def post(self):
        key = self.get_argument('key')
        attr = self.get_argument('attr')
        next = self.get_argument('next', '/')

        blob_key = re.findall(r'blob-key="*(\S+)', self.request.body)[0]
        blob_info = blobstore.BlobInfo.get(blob_key)
        entity = db.get(key)
        setattr(entity, attr, blob_info)
        entity.put()
        return self.redirect(next)

class UploadForm(BaseHandler):
    def get(self):
        redirect = '/upload?' + urllib.urlencode({
            'key': self.current_site.key(),
            'attr': 'default_gravatar'
        })
        upload_url = blobstore.create_upload_url(redirect)
        ...