1) install
pip install venv
pip install pipenv
pip install virtualenv
pip install virtualenvwrapper

pip install -i https://pypi.douban.com/simple pip -U
pip install -i https://pypi.douban.com/simple pipenv -U
pip install -i https://pypi.douban.com/simple virtualenv -U
pip install -i https://pypi.douban.com/simple virtualenvwrapper -U

2) setting
vi ~/.bashrc
export WORKON_HOME='~/.virtualenvs'
source /usr/local/bin/virtualenvwrapper.sh

3) create env
mkvirtualenv flask

4) swithc env
workon flask

5) deactivate env
deactivate

5) remove env
rmvirtualenv flask