I fail to see any logic in the explanation given at #765022. So, because of infinitesimal number of users who, for some weird reasons, want to install Python3 interpreter from source, everyone else has to just symlink /usr/local/ site-packages and /usr/local/dist-packages together, breaking *both* the standard approach described in the upstream documentation, and your "sophisticated" separation scheme. This is what I did just now, as I needed to install a third-party app with its provided setup.py, the author of which surely was able to read official docs and so the libs used by the app and built from the source naturally fell into /usr/local/lib/site-extensions. The fact I used Debian-provided Python3 interpreter for this task doesn't make those libs "provided by Debian distributive", they are NOT.
