(autoload 'python-mode "python-mode" "Python Mode." t)
 (add-to-list 'auto-mode-alist '("\.py\'" . python-mode))
 (add-to-list 'interpreter-mode-alist '("python" . python-mode))

;; by default, the function 'python-mode is associated with
;; the package python.el. The following changes that to python-mode.el:
(autoload 'python-mode "python-mode" "Python Mode." t)

;; open py files with python-mode
(add-to-list 'auto-mode-alist '("\.py\'" . python-mode))

;; sets python interpreter mode to be python-mode
(add-to-list 'interpreter-mode-alist '("python" . python-mode))