View and insert possible Python completions in the editor using
Ctrl-Alt-Space.
You must have the Python module 'jedi' installed:
(sudo) pip install jedi
If you have multiple python installations (e.g. python2 and python3), you can select which python has jedi installed in the settings.
NB: Atom has a known bug where settings sometimes won't appear until after a package has been activated at least once. If you don't see a place to specify the path to your prefered python executable in the settings, try to trigger autocomplete-jedi and then check again.