Being more familiar with Python then elisp, I'd like to evaluate the selection as as Python snipped - as a short-cut to opening a calculator or Python prompt and copy-pasting between them.

Is there a convenient way to evaluate the selection as a Python expression?

So I could type for eg 11**13//7 and replace it with 4931816020561

  • python-mode.el available at Melpa comes with a variable py-return-result-p - when t it stores the result in kill-ring. From there replace an active-region with. Nov 22, 2017 at 7:22

2 Answers 2


Just select your code and then

C-u M-|   python


C-u M-x shell-command-on-region   python
  • This outputs (Shell command succeeded with no output) unless you add print() around every expression.
    – ideasman42
    Nov 23, 2017 at 14:14
  • of course you need to print the result
    – djangoliv
    Nov 23, 2017 at 14:20
  • Not necessarily, this can be setup so the result is always printed.
    – ideasman42
    Nov 23, 2017 at 15:00

Posting own answer which mostly works as I'd like (needed some special consideration for evil mode).

While it works well for basic usage, errors will also replace the selection, ideally a nonzero exit code would display as a message instead of putting the error into the editor.

;; See: https://emacs.stackexchange.com/a/34900/2418
;; Wrapper for 'shell-command-on-region', keeps the selection.
(defun shell-command-on-region-and-select
    (start end command &optional
           output-buffer replace
           error-buffer display-error-buffer
  "Wrapper for 'shell-command-on-region', re-selecting the output.

Useful when called with a selection, so it can be modified in-place"
  (let ((buffer-size-init (buffer-size)))
     start end command output-buffer replace
     error-buffer display-error-buffer
    (setq deactivate-mark nil)
    (setq end (+ end (- (buffer-size) buffer-size-init)))
    (set-mark start)
    (goto-char end)
    ;; needed for evil line mode
    (when (string= evil-state "visual")
      (when (eq (evil-visual-type) evil-visual-line)
        (evil-visual-select start end 'line)))))

(defun eval-region-as-py ()
  "Evaluate selection as a python expression, replacing it with the result"
   "python -c 'import sys; sys.stdout.write(str((eval(sys.stdin.read()))))'" 0 t))

(define-key evil-visual-state-map (kbd "RET") 'eval-region-as-py)

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