title: How to downgrade the python on macbook from 3.8 to 3.5
body: <p>I've tried several ways to downgrade the python3, including using pyenv, but it has the build failed error. I think it's probably because my python3 is in my usr/bin folder and I can not delete it. For the course requirement, I really need to downgrade python to 3.5. Is there any way to do so?</p>