[Python 3] Python version management with virtual environment

1. virtualenv (On windows)

• Install
  : pip install virtualenv
• Create a folder
  : virtualenv venv
• Activate a virtualenv
  : .\venv\Scripts\activate
• Deactivate
  : Deactivate
• Previous version
  : virtualenv venv --python=python3.5

2. pyvenv (manage multiple python 3.3 or later version)

3. autoenv

 automatically execute virtual environment