Use Cloud Vision API in webapp2: ImportError: cannot import name cygrpc

Question

I want to use Google Cloud Vision label detection in a simple App Engine webapp2 project. ( combine https://github.com/GoogleCloudPlatform/python-docs-samples/tree/master/vision/cloud-client/quickstart and https://github.com/GoogleCloudPlatform/python-docs-samples/tree/6f5f3bcb81779679a24e0964a6c57c0c7deabfac/appengine/standard/hello_world). when the app is deployed to app engine "ImportError: cannot import name cygrpc" is produced and fails import "from google.cloud import vision", even after adding "grpcio==1.25.0" to the requirements.txt file the error remains.

quickstart.py

import webapp2
import io
import os

from google.cloud import vision
from google.cloud.vision import types

class MainPage(webapp2.RequestHandler):
    def get(self):
        client = vision.ImageAnnotatorClient()
        file_name = os.path.abspath('resources/wakeupcat.jpg')
        
        with io.open(file_name, 'rb') as image_file:
            content = image_file.read()
        
        image = types.Image(content=content)
        
        response = client.label_detection(image=image)
        labels = response.label_annotations
        
        print('Labels:')
        for label in labels:
           print(label.description)
           
        
app = webapp2.WSGIApplication([
    ('/', MainPage),
], debug=True)

requirements.txt

google-cloud-vision==0.39.0

app.yaml

runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: quickstart.app

libraries:
- name: ssl
  version: latest

appengine_config.py

from google.appengine.ext import vendor
vendor.add('lib')

Created resources folder with wakeupcat.jpp. And then created lib folder "pip install -r requirements.txt -t lib" to install the libraries.