python code completion in Emacs

You want to activate the auto-complete mode in the context where you get that message, either

• every time you open python files, by adding the following to your .emacs:

  (add-hook 'python-mode-hook
    (lambda ()
           (auto-complete-mode 1)))
  

• or when you open any file, by adding the following to your .emacs:

  (global-auto-complete-mode t)
  

The question you're linking to suggests something even more complete (i.e. which subsumes the first of the two additions I suggest):

(add-hook 'python-mode-hook
      (lambda ()
             (auto-complete-mode 1)
             (set (make-local-variable 'ac-sources)
                  (append ac-sources '(ac-source-rope) '(ac-source-yasnippet)))
             (set (make-local-variable 'ac-find-function) 'ac-python-find)
             (set (make-local-variable 'ac-candidate-function) 'ac-python-candidate)
             (set (make-local-variable 'ac-auto-start) nil)))

Those additions will be needed to get full completion using snippets and Rope.