Exploring Python Ligatures

So ligature support is built in to emacs, via prettify-symbols-mode. This means we just need to activate this along with python-mode, and then define some symbols to replace.

My target is to have ligatures enabled for python mode only, rather than globally, which means global-prettify-symbols-mode is not the answer.

By default, in python mode, prettify-symbols replaces lambda, and, and or with symbols (check the buffer local variable prettify-symbols-alist for the current value in a buffer). Let's add a few more symbols. From this aliquote blog post, there's a few suitable suggestions:

    (defun add-python-mode-symbols ()
	    (mapc (lambda (pair) (push pair prettify-symbols-alist))
	     '(
		("->" . 8594)
		("=>" . 8658)
		("<=" . 8804)
		(">=" . 8805)
		("<-" . 8592)
		("!=" . 8800)
		)))

    (add-hook 'python-mode-hook (lambda ()
				  (add-python-mode-symbols)
				  (prettify-symbols-mode t)
				  ))

This modern emacs blog post describes using describe-char and insert-char to work out the number needed for a particular symbol, and the use of mapc for adding the symbols in a sensible manner. I've opted to isolate the definitions in a function to make it a little more transparent what is being added to the python hook. I think (but haven't confirmed) that the symbols list needs to be defined before enabling prettify-symbols-mode.