Emacs python-mode problem

[Chunyu]

While debugging a C/C++ program with GDB in emacs (version 21.3.50),
there is an arrow symbol `=>' in the source window to indicate the
current line normally. But After I load the python-mode.el file from
my ~/.emacs.el, the arrow symbol disappear while debugging with GDB in
emacs. (The python-mode.el is from
http://www.python.org/emacs/python-mode, version 4.6.)

I load the python in my ~/.emacs.el by
(require 'python-mode)
(setq auto-mode-alist
      (cons '("\\.py$" . python-mode) auto-mode-alist))
(setq interpreter-mode-alist
      (cons '("python" . python-mode) interpreter-mode-alist))

Now, I have to comment these lines, and load python-mode.el by hand
when I want to use python-mode. How can I solve it? Is there another
better python-mode code? Thanks for your replay.