$ python3 -m pip install --upgrade py4web
works fine (apparently, no errors), but I can't find py4web-start.py. I looked in the site-packages directory where py4web is installed, but couldn't find py4web-start.py.
I was able to copy py4web-start.py from the git repo to a new directory, then run with
$ python3 py4web-start.py apps
and it worked fine. The documentation seems to indicate that py4web-start.py is installed automatically in a location in the path.