Python3
Hi, i am running on a Ubuntu system and i have troubles with running python 3.6.5 and i can't use this package... while i was using windows it worked fine for me (the last time i used it).

It seems that something is wrong with your environment path. Can you call just python in a terminal to run it? And @xovertheyearsx may help you with problems on linux.
It still works in linux with 2 and 3. By default, as of Ubuntu 17.10, they use python 3 even though some packages still require 2. So if youre using LTS 18.04.x, depending on your installation, it may b 2 or 3. Usually its 3 until I explicitly install 2. The path is handled by default in Linux. So all you need to do is find out in the terminal which one it is. If it is 2, you can just specify python3 in settings. I explained how to do do this in the user documentation in the Wiki.
See also https://github.com/foreshadow/atom-python-run/issues/117 . I found this out by chance. python is not in PATH on Ubuntu 18.04, but python3 is. You could create a symlink yourself or change the interpreter in package (atom-python-run) settings (F5 command), except I am unable to get those settings working on Linux (that is what https://github.com/foreshadow/atom-python-run/issues/117 is about).