This is a reference repository showing how to use Travis CI with:
The approach is to fetch a C++17 compiler (e.g. g++7) and Python 3.7 with special apt-sources, then building OpenMPI from source with this compiler, which results in a C++17 compatible MPI compiler. Finally, mpi4py is installed, being told about this new MPI compiler.
Additionally, because building MPI from source takes quite some time (10+ minutes), the installation is cached between each build. This means the MPI installation only has to be built once, and is reused the rest of the time, which saves time.
See .travis.yml for the how to do this!