OK, I 've set to python3.6 via
root@carbon nik # eselect python list
Available Python interpreters, in order of preference:
[1] python3.4
[2] python2.7
[3] python3.6 (fallback)
[4] python3.5 (fallback)
root@carbon nik # eselect python set 3
root@carbon nik # eselect python show
python3.6
and it worked. Thank you for the hints!