
how to install a Python 3.7 library using pip. 
In order to follow best practices, install the new library in a virtual environment:

    python3 -m venv py3.7.4-env
    source py3.7.4-env/bin/activate
    pip install --upgrade pip

First line from the above will create a virtual environment named py3.7.4-env. 
Second line will activate the environment. 
Last line will update the local pip package manager. 


Once en environment is activated, you can simply use the python and pip commands. 
Any modifications you do inside an environment will have effect only in the 
respective environment, 
the global installed Python interpreter and libraries will not be affected.

    for example:
    pip install Pillow
