OK, I figured this out.
In the source directory there is a file setup.py. To build and install mmpython, give the command './setup.py build' and './setup.py install'.
I struggled with this package for a while last night, and even ran the setup.py script. But I ran it without the build or install commands, and so it just exited with a message telling me to use --help or --help-commands. This morning in the light of day, somewhat better rested, I ran setup.py with the --help and --help-commands options, and recognized my mistake. Now I will know for next time.