Flit-core is the distribution-building parts of Flit (a packaging tool for simple Python modules).
Build the package:
pip3 wheel -w dist --no-cache-dir --no-build-isolation --no-deps $PWD
Install the package:
pip3 install --no-index --find-links dist flit_core
The meaning of the pip3 configuration options and commands:
This command builds the wheel archive for this package.
-w
              dist
            
                Instructs pip to put the created wheel into the dist directory.
              
--no-cache-dir
            
                Prevents pip from copying the created wheel into the
                /root/.cache/pip directory.
              
This command installs the package.
--no-build-isolation, --no-deps, and --no-index
            These options prevent fetching files from the online package repository (PyPI). If packages are installed in the correct order, pip won't need to fetch any files in the first place; these options add some safety in case of user error.
--find-links
              dist
            
                Instructs pip to search for wheel archives in the
                dist directory.