init.el

(make-face 'font-lock-number-face)
(set-face-attribute 'font-lock-number-face nil :inherit font-lock-constant-face)
(setq font-lock-number-face 'font-lock-number-face)
(defvar font-lock-number "[0-9-.]+\\([eE][+-]?[0-9]*\\)?")
(defvar font-lock-hexnumber "0[xX][0-9a-fA-F]+")
(defun add-font-lock-numbers (mode)
  (font-lock-add-keywords mode `(
                                 (,(concat "\\<\\(" font-lock-number "\\)\\>" ) 0 font-lock-number-face)
                                 (,(concat "\\<\\(" font-lock-hexnumber "\\)\\>" ) 0 font-lock-number-face)
                                 )))

usage:

(add-font-lock-numbers `python-mode)