Re: [BUG] shell sessions started outside of Babel broken

[Jack Kamm]

Jack Kamm <jackkamm@tatersworld.org> writes:

> I think it's worthwhile for Org Babel to support external sessions
> where feasible.  ob-R and ob-python have long supported this, though
> recent changes to ob-python seem to have broken it there (I'm looking
> into fixing that).

I'm attaching a patch that restores ob-python's ability to work with
externally started sessions.

I'll plan to push this commit in a few days, unless any problems with
the patch are noticed.

>From 47bf309b9af4cd342d3e939442504a9d34bf6592 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Sat, 25 Mar 2023 07:53:28 -0700
Subject: [PATCH] ob-python: Allow working with externally started sessions
 again

* lisp/ob-python.el (python-shell-buffer-name): Remove unneeded
defvar.
(org-babel-python-initiate-session-by-key): Check if session already
existed before run-python.  Only wait for initialization if it's a
newly started session.  Also simplify the code a bit by combining
multiple setq and let statements into a single let statement.  Also
add a comment about why adding to `python-shell-first-prompt-hook'
after `run-python' should be safe from race conditions.
---
 lisp/ob-python.el | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/lisp/ob-python.el b/lisp/ob-python.el
index 456f2d489..0e0539d7a 100644
--- a/lisp/ob-python.el
+++ b/lisp/ob-python.el
@@ -169,7 +169,6 @@ (defun org-babel-python-without-earmuffs (session)
        (substring name 1 (- (length name) 1))
       name)))
 
-(defvar python-shell-buffer-name)
 (defvar-local org-babel-python--initialized nil
   "Flag used to mark that python session has been initialized.")
 (defun org-babel-python-initiate-session-by-key (&optional session)
@@ -178,27 +177,33 @@ (defun org-babel-python-initiate-session-by-key 
(&optional session)
 then create.  Return the initialized session."
   (save-window-excursion
     (let* ((session (if session (intern session) :default))
-           (py-buffer (org-babel-python-session-buffer session))
+           (py-buffer (or (org-babel-python-session-buffer session)
+                          (org-babel-python-with-earmuffs session)))
           (cmd (if (member system-type '(cygwin windows-nt ms-dos))
                    (concat org-babel-python-command " -i")
-                 org-babel-python-command)))
-      (unless py-buffer
-       (setq py-buffer (org-babel-python-with-earmuffs session)))
-      (let ((python-shell-buffer-name
-            (org-babel-python-without-earmuffs py-buffer)))
-       (run-python cmd)
-        (with-current-buffer py-buffer
-          (add-hook
-           'python-shell-first-prompt-hook
-           (lambda () (setq-local org-babel-python--initialized t))
-           nil 'local)))
-      ;; Wait until Python initializes.
-      ;; This is more reliable compared to
-      ;; `org-babel-comint-wait-for-output' as python may emit
-      ;; multiple prompts during initialization.
+                 org-babel-python-command))
+           (python-shell-buffer-name
+           (org-babel-python-without-earmuffs py-buffer))
+           (existing-session-p (comint-check-proc py-buffer)))
+      (run-python cmd)
       (with-current-buffer py-buffer
-        (while (not org-babel-python--initialized)
-          (org-babel-comint-wait-for-output py-buffer)))
+        ;; Adding to `python-shell-first-prompt-hook' immediately
+        ;; after `run-python' should be safe from race conditions,
+        ;; because subprocess output only arrives when Emacs is
+        ;; waiting (see elisp manual, "Output from Processes")
+        (add-hook
+         'python-shell-first-prompt-hook
+         (lambda () (setq-local org-babel-python--initialized t))
+         nil 'local))
+      ;; Don't hang if session was started externally
+      (unless existing-session-p
+        ;; Wait until Python initializes
+        ;; This is more reliable compared to
+        ;; `org-babel-comint-wait-for-output' as python may emit
+        ;; multiple prompts during initialization.
+        (with-current-buffer py-buffer
+          (while (not org-babel-python--initialized)
+            (org-babel-comint-wait-for-output py-buffer))))
       (setq org-babel-python-buffers
            (cons (cons session py-buffer)
                  (assq-delete-all session org-babel-python-buffers)))
-- 
2.39.2