This is a quick and dirty repl hack for emacs -- i.e. use it when AFK and need to show people REPL-based development without a huge setup hassle.

;; emacs -Q
;; then paste in the commands below
;; then M-x eval-buffer
;; then M-x shell and run python or whatnot
;; then C-x o back to scratch buffer
;; then M-x python-mode or whatnot

(defun send-region-to-shell(start end)
  (interactive "r")
  (append-to-buffer (get-buffer "*shell*") start end)
  (execute-kbd-macro (read-kbd-macro "M-w C-x o C-m C-x o"))
  )
(global-set-key (kbd "C-c r") 'send-region-to-shell)

(defun send-line-to-shell ()
  (interactive)
  (execute-kbd-macro (read-kbd-macro "C-a C-SPC C-e C-c r"))
  )
(global-set-key (kbd "C-c l") 'send-line-to-shell)

;; https://stackoverflow.com/questions/2081577/emacs-split-horizontal
(setq split-height-threshold nil)
(setq split-width-threshold 0)