Which version of Python are you running with? Please note that Panda3D on Ubuntu is built with the default version of Python, which is 2.7 on Ubuntu.
This error also comes up if you have a file called panda3d.py or panda3d/init.py that conflicts with Panda3D’s own panda3d package.
I’m not sure where you read to use ‘pandac’ instead; this is deprecated and is unlikely to solve your problem in this case.