I have no experience with your software mix, but FYI, Ubuntu 18.04 has available both Python 2 and 3. The default may not have what you want, but to illustrate, what do you see from:
apt search python | egrep '^(python[.][0-9]-minimal)'
The package might already be installed, but the path used to specify might need to specify which release. Or the package might not be installed, and getting it would be as simple as installing the other release (leaving the old one still installed), and then specifying to use python3.