Install instructions on Google Colaboratory
The provided instructions didn't work for me to install python3-graph-tool on Google Colab, but the following does work:
!apt-key adv --keyserver keys.openpgp.org --recv-key "612DEFB798507F25"
!add-apt-repository "http://downloads.skewed.de/apt/"
!apt-get install python3-graph-tool