From one-line list to one element per line in python-mode

Question

How do I turn a long one-line list, such as

test_list = ['a0000000', 'b1111111', 'c2222222', 'd3333333', 'e4444444', 'f5555555', 'g6666666']

into a one element per line list:

test_list = ['a0000000',
             'b1111111',
             'c2222222',
             'd3333333',
             'e4444444',
             'f5555555',
             'g6666666']

Or:

test_list = [
    'a0000000',
    'b1111111',
    'c2222222',
    'd3333333',
    'e4444444',
    'f5555555',
    'g6666666',
]

With fill-paragraph long one-line lists are at least broken up into multiline lists:

test_list = ['a0000000', 'b1111111', 'c2222222', 'd3333333',
             'e4444444', 'f5555555', 'g6666666' ]

But I would find a one element per line list in many cases more useful. Is anyone aware of such a elisp function (e.g. in elpy or anywhere else)?

Answer 1

You can always write a function to do what you want and bind it to a key sequence. The following will deal with the vast majority of cases, but it will fail if a list element contains the string ", ". It assumes that your cursor is at the beginning of the line in question (and leaves point unchanged), searches for the string ", " in the line and calls newline after each one (which deals intelligently with the space-to-newline conversion). It then calls indent-region between the original point and the final end-of-line, to reindent everything properly. It will also work on multi-line lists (e.g. the two-line list after M-q) although you will have to call it once on each line:

(defun python-list-break-and-indent ()
  "Convert a single-line list into a block list, indented properly.
   ASSUMPTION: the only occurrences of the string \", \" are between
   list elements."
  (interactive)
  (save-excursion
    (let ((beg (point)))
      (while (search-forward ", " (save-excursion (end-of-line) (point)) t)
        (newline))
      (end-of-line)
      (indent-region beg (point)))))

(define-key python-mode-map (kbd "C-c b") #'python-list-break-and-indent)

I bound the function to C-c b because it was undefined in python-mode-map in my case, but you should check with C-h c C-c b in a python mode buffer and choose something else if it is taken (C-c <letter> keys are supposed to be reserved for users).