pyenv:
powershell as administrator:
Set-ExecutionPolicy RemoteSigned
Invoke-WebRequest -UseBasicParsing -Uri "https://raw.githubusercontent.com/pyenv-win/pyenv-win/master/pyenv-win/install-pyenv-win.ps1" -OutFile "./install-pyenv-win.ps1"; &"./install-pyenv-win.ps1"
pyenv --version

never: Set-ExecutionPolicy Restricted

---

Install Python 3
then
pip3 install virtualenv

cd myvirtual_p3
virtualenv.exe myvirtual

Install Python 2.7
then
cd myvirtual_p2
virtualenv -p C:\Python27\python.exe myvirtual

pyenv:
https://github.com/pyenv-win/pyenv-win
venv:
https://github.com/pyenv-win/pyenv-win-venv

cd myvirtual\Scripts
activate.bat