I need this to test half-installed socket-activated python
script, which requires PYTHONPATH and LD_LIBRARY_PATH set.
I assume that other people might find it useful to.

-E VAR passes through VAR from the environment, while
-E VAR=value sets VAR=value.

systemd-activate -E PYTHONPATH=/var/tmp/inst1/usr/lib64/python3.3/site-packages -E LD_LIBRARY_PATH=/var/tmp/inst1/usr/lib -l 2000 python3 -c 'from systemd.daemon import listen_fds; print(listen_fds())'