如何使用python flask从谷歌云存储服务图像

我使用了GoogleAppEngineCloudStorageClientPython库并使用类似于以下示例的代码加载了图像:

from google.appengine.api import app_identity
import cloudstorage
from flask import Flask, send_file
import io, os

app = Flask(__name__)

# ...

@app.route('/imagetest')
def test_image():

  # Use BUCKET_NAME or the project default bucket.
  BUCKET_NAME = '/' + os.environ.get('MY_BUCKET_NAME',
                                     app_identity.get_default_gcs_bucket_name())
  filename = 'mytestimage.jpg'
  file = os.path.join(BUCKET_NAME, filename)

  gcs_file = cloudstorage.open(file)
  contents = gcs_file.read()
  gcs_file.close()

  return send_file(io.BytesIO(contents),
                   mimetype='image/jpeg')