Thank you guys!
Changing the symlink helped.
I just installed 0.37.1 aio a few days ago.
Did the libcec installiton as described here https://home-assistant.io/components/hdmi_cec/
Did the update to 0.38.2
Couldn’t get cec to run.
ImportError: No module named ‘cec’
matt-cahill comment at https://github.com/home-assistant/fabric-home-assistant/issues/44
finally helped to understand and to solve it.
Changing the sym link from within the venv fixed the problem.
homeassistant@raspberrypi:/home/pi$ source /srv/homeassistant/homeassistant_venv/bin/activate
ln -sf /usr/local/lib/python3.4/site-packages/cec /srv/homeassistant/homeassistant_venv/lib/python3.4/site-packages