To start a virtual python environment for testing, development and installation of packages/modules with pip separate from the os or user level, follow these instructions:

Main installation of venv if not already installed:

sudo apt install python3-venv

Create and activate the venv:

python -m venv directory-of-venv
cd directory-of-venv/bin/  
source activate  

Deactivate the venv:

deactivate