[graph-tool] Installing graph-tool

I'm on Ubuntu 18.04 and trying to install this to use in anaconda Pycharm editor, following the instructions mentioned for ubuntu here https://git.skewed.de/count0/graph-tool/wikis/installation-instructions#nati... trying the three DISTRIBUTION none is working,and trying to verify the package using both keys, whether the mentioned in the link or that one in the mailing list: 612DEFB798507F25 or 7A80C8ED4FCCBE09 it gives: gpg: keyserver receive failed: No keyserver available and definitely the result of apt-get install ... is : E: Unable to locate package python3-graph-tool -- Sent from: http://main-discussion-list-for-the-graph-tool-project.982480.n3.nabble.com/