I wrote up this keybinding the other day at work, and found that I missed it when I went home, so I wrote it again from scratch.
It allows you easily indent or undent the current region using M-left and M-right:
(global-set-key [M-left] '(lambda () (interactive)
(save-excursion
(py-shift-region-left (region-beginning) (region-end)))))
(global-set-key [M-right] '(lambda () (interactive)
(save-excursion
(py-shift-region-right (region-beginning) (region-end)))))