This issue is still true for 3.8.0b1, Ubuntu 19.04, umask is 0077, Python 3.8 is installed using "sudo make install".

!bin/python
bin/python setup.py develop
running develop
running egg_info
writing fs.webdavfs.egg-info/PKG-INFO
writing dependency_links to fs.webdavfs.egg-info/dependency_links.txt
writing entry points to fs.webdavfs.egg-info/entry_points.txt
writing requirements to fs.webdavfs.egg-info/requires.txt
writing top-level names to fs.webdavfs.egg-info/top_level.txt
error: [Errno 13] Permission denied: '/opt/python-3.8.0b1/lib/python3.8/lib2to3/Grammar3.8.0.beta.1.pickle'


So "python3 -m venv" should setup a virtualenv properly without the need writing anything to the Python installation directory. Or it is up to "make install" to generate the related files properly during installation.