Google app engine unable to use python 3

[Gary Ng]

I've following the instruction in: https://cloud.google.com/appengine/docs/flexible/python/quickstart

But when I execute "python" the version number still show 2.7.9, I've checked the app.yaml, it already set the python_version: 3

[Gary Ng]

[Kenworth (Google Cloud Platform)]

The app.yaml holds the configuration settings for your application. Setting it to 'python_version: 3' tells your app to use version 3 for your application. Your development environment, however, may have a different version of Python running (or none at all). 

Example: To run Python 3 in Windows, make sure:

1- Python 3 is installed (run 'python --version')

2- Configure environment variables to use Python 3