$ pip3 install virtualenv
$ virtualenv venv
$ source venv/bin/activate
$ deactivate
(venv) $ pip3 install -r requirements.txt
or
(venv) $ pip3 install urllib3
(venv) $ pip3 install schedule
- after installed new library, you need to update requirements.txt
(venv) $ pip3 freeze | tee requirements.txt
``