While I'm not trying to apportion blame here, it should be noted that a much simpler fix would be to simply deletepyproject.toml. The reason this isn't possible appears to be because projects likeblackchose to use that file for their general configuration, which is arguably allowed by PEP ...
Command line: virtualenv -p python3.7 env source env/bin/activate pip install -U pip pip install --use-feature=2020-resolver --use-feature=fast-deps -v cython This works correctly on my home linux computer, but fails at work where we have the following /etc/pip.conf: ...