org-src-mode send commands to repl in named python :session, not *Python*

Question

Is there a method to set what buffer python-mode looks to for a running python process?

I have a babel block in org-mode like

#+BEGIN_SRC python :session session1
import os
os.uname()
#+END_SRC

I can run the block (C-cC-c). I get results and a new *session1* buffer.

But I want to tinker with the code in the block. So I open it in a new buffer with the cord C-C C-' and am in org-src-mode ("OrgSrc") and python major mode (C-h b shows, for example, bindings for python-shell-send-region). However, attempting to use these bindings instead throws the warning:

Start a python process first with 'M-x run-python' or 'C-c C-p'.

Python is running, but it's in *session1*. If I do not name the :session the buffer is *Python* and all works as expected.

And, if i follow the run-python suggestion, a new *Python* buffer is created which is obviously not the same session in which the first execution occurred.

In addition to potentially having a need for separate sessions on a single host, I am tinkering with this simplified example in an effort to have a more usable python mode when interacting with tramp/:dir. e.g.

#+BEGIN_SRC python :session :dir /HostB:/tmp/
import os
os.uname()
#+END_SRC

I've also tried ob-ipython but I'm not sure configuring it to work with remote hosts is feasible.

Answer 1

This is really hidden and (to my knowledge) not documented so caveat emptor …

At the very end of org-edit-src-code I found the following snippet:

(let ((edit-prep-func (intern (concat "org-babel-edit-prep:" lang))))
  (when (fboundp edit-prep-func)
    (funcall edit-prep-func babel-info)))

This means you can define your own function org-babel-edit-prep:python and it will get executed after the Org Src buffer has been set up. It will receive as argument babel-info which is (per the doc string for org-babel-get-src-block-info) a list like (language body arguments switches name start coderef).

So … I use the following code to tell the new buffer where to look for the python process:

(defun org-babel-edit-prep:python (babel-info)
  "Set the buffer-local value of `python-shell-buffer-name' based
  on the :session header."
  (let* ((babel-args (nth 2 babel-info))
         (session (alist-get :session babel-args)))
    (when (string-match "\\*\\(.*\\)\\*" session)
      (setq-local python-shell-buffer-name (match-string 1 session)))))

NOTE: I haven't tested this with remote connections, though I assume something similar could be made to work.

Answer 2

The best workaround I've found so far is isend-mode. No python completion or inspection, but at least lines are easily sent to the REPL (isend-send/C-RET)

Answer 3

I've found a much simpler (if somewhat more primitive) solution:

If you use pyvenv in your sessions like I do, and already need to have an emacs-lisp block before your python sessions anyways, it's pretty easy to just do something like this:

#+begin_src emacs-lisp :session session1
  (pyvenv-activate "~/foo/path_to_my_venv")
  (setq python-shell-buffer-name "session1")
#+end_src

#+begin_src python :session session1
  import os
  os.uname()
#+end_src