Installing from PyPI with pip: Open a terminal and enter your virtual environment
Execute sudo apt install libgirepository1.0-dev gcc libcairo2-dev pkg-config python3-dev gir1.2-gtk-4.0 to install the build dependencies and GTK
Execute pip3 install pycairo to build and install Pycairo
Execute pip3 install PyGObject to build and install PyGObject
Change the working directory to where your hello.py script can be found
Run python3 hello.py