The autocomplete function (TAB) on Newpyter is working very slowly for me, making it practicable unusable.

I found that is a known issue with a package named Jedi.

You can solve this problem by adding the following magic line in your notebook:

%config Completer.use_jedi = False

Or solve it permanently by creating a ipython profile following these instructions.

I don't what we lose disabling Jedi, but I found autocomplete so important, that it might be good to disable it by default.