Python 3 is available within Domino. You can use the Compute Environment we provide in our cloud system (for private deployments, please contact us if you don't already have an environment set up for this purpose).
You can access your Compute Environment by clicking on Settings in the left hand panel, from there you should see:
Then you can click on the drop down menu to see what environments are available, Python 3 is listed here:
Now when you select this environment, your Python scripts will be using the Python 3 version.
Also, we now have both Python 2 and Python 3 kernel options, as well:
Since Python 3 is fairly new, you can use pip freeze in your Jupyter notebook to see what packages are currently installed in the Python 3 environment. You can also put this at the beginning of your script, as well.
If a package(s) you need is currently not on the list, you can install them yourself via the methods mentioned here How Can I Install Packages and Dependencies
Also, if you feel comfortable you can also modify your Dockerfile as needed using these instructions: How to Avoid Re-installing Packages in Each Run . This way your packages and dependencies will be cached and won't have to be run each time when you start a new session.