Virtual Environment

create virtual environment 'my-env'

virtualenv my-env

start virtual environment

source my-env/bin/activate

end virtual environment

deactivate

set default python version for virtual environment

virtualenv -p /usr/bin/python3.7 my-env

change python version of virtual environment

virtualenv --python=/usr/bin/python3.7 my-env

install package in venv with python 3

pip3 install <package>[==<version>]
or 
sudo <path-to-venv>/bin/python3.7 -m pip install <package>[==<version>]

Install GDAL in venv:

pip3 install --global-option=build_ext --global-option="-I/usr/include/gdal" GDAL==`gdal-config --version`

Activate virtual environment in python3 script

#!/usr/bin/python3
activate_this = '/local/www/venv-python3.7-django3.1/bin/activate_this.py'
with open(activate_this) as file_:
       exec(file_.read(), dict(__file__=activate_this))