Maybe you don't need `pyenv` and/or `virtualenv` in most cases.
## Install Python
> Don't have `brew`? Go to <https://brew.sh>.
```
brew install python3
```
If you still need Python 2, run `brew install python`.
## Install Jupyter Notebook
```
pip3 install jupyter
python3 -m ipykernel install --user
```
You also want Python 2 kernel, so then:
```
pip install ipykernel
python -m ipykernel install --user
```
That's all.
# How about `virtualenv`?
Since Python 3 got its own virtual environment tool called [venv](https://docs.python.org/3/library/venv.html), You no longer need `virtualenv` itself.