Emacs bulk indent for Python

Question

If you are programming Python using Emacs, then you should probably be using python-mode. With python-mode, after marking the block of code,

C-c > or C-c C-l shifts the region 4 spaces to the right

C-c < or C-c C-r shifts the region 4 spaces to the left

If you need to shift code by two levels of indention, or some arbitary amount you can prefix the command with an argument:

C-u 8 C-c > shifts the region 8 spaces to the right

C-u 8 C-c < shifts the region 8 spaces to the left

Another alternative is to use M-x indent-rigidly which is bound to C-x TAB:

C-u 8 C-x TAB shifts the region 8 spaces to the right

C-u -8 C-x TAB shifts the region 8 spaces to the left

Also useful are the rectangle commands that operate on rectangles of text instead of lines of text.

For example, after marking a rectangular region,

C-x r o inserts blank space to fill the rectangular region (effectively shifting code to the right)

C-x r k kills the rectangular region (effectively shifting code to the left)

C-x r t prompts for a string to replace the rectangle with. Entering C-u 8 <space> will then enter 8 spaces.

PS. With Ubuntu, to make python-mode the default mode for all .py files, simply install the python-mode package.

In addition to indent-region, which is mapped to C-M-\ by default, the rectangle edit commands are very useful for Python. Mark a region as normal, then:

• C-x r t (string-rectangle): will prompt you for characters you'd like to insert into each line; great for inserting a certain number of spaces
• C-x r k (kill-rectangle): remove a rectangle region; great for removing indentation

You can also C-x r y (yank-rectangle), but that's only rarely useful.

indent-region mapped to C-M-\ should do the trick.

I've been using this function to handle my indenting and unindenting:

(defun unindent-dwim (&optional count-arg)
  "Keeps relative spacing in the region.  Unindents to the next multiple of the current tab-width"
  (interactive)
  (let ((deactivate-mark nil)
        (beg (or (and mark-active (region-beginning)) (line-beginning-position)))
        (end (or (and mark-active (region-end)) (line-end-position)))
        (min-indentation)
        (count (or count-arg 1)))
    (save-excursion
      (goto-char beg)
      (while (< (point) end)
        (add-to-list 'min-indentation (current-indentation))
        (forward-line)))
    (if (< 0 count)
        (if (not (< 0 (apply 'min min-indentation)))
            (error "Can't indent any more.  Try `indent-rigidly` with a negative arg.")))
    (if (> 0 count)
        (indent-rigidly beg end (* (- 0 tab-width) count))
      (let (
            (indent-amount
             (apply 'min (mapcar (lambda (x) (- 0 (mod x tab-width))) min-indentation))))
        (indent-rigidly beg end (or
                                 (and (< indent-amount 0) indent-amount)
                                 (* (or count 1) (- 0 tab-width))))))))

And then I assign it to a keyboard shortcut:

(global-set-key (kbd "s-[") 'unindent-dwim)
(global-set-key (kbd "s-]") (lambda () (interactive) (unindent-dwim -1)))