Okay, I have switched to the master branch now and rebuild emacs.
So I find it works differently than I thought. As reported in my original bug-report,
the comint still does not show the output when sending using `C-c C-c` but I see now
that actually that is bound to `python-shell-send-buffer`. So now I notice that the only
function that effects in the comint printing the output is `python-shell-send-statement`.
Probably I was misled by the Spacemacs function `pyhton-shell-send-line` which uses
`python-shell-send-region` and therefore when used the comint does not print the output.
(And I was blindly assuming that `C-c C-c` was using shell send line/statement)
Thanks for your replies!