How do I set Emacs tab size to 4 chars wide for .py files?

I've tried using the following:

(setq-default tab-width 4)
(setq-default tab-stop-list (list 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60))

But the size of tabs when editing .py files is still 8 chars wide. In other files it has gone down to 4, so I assume the Python major mode is overriding this somehow. I see that I can set python-indent to 4, but this causes spaces to be inserted (which goes against our code style guide).

How do I make the tabs 4 chars in width?

Update:

I've also tried this, but it didn't do anything:

(add-hook 'python-mode-hook
  (setq indent-tabs-mode t)
  (setq tab-width 4)
)