[PATCH] Change default ob-python session command to match run-python

[Jack Kamm]

The attached patch changes the default behavior of ob-python sessions,
to respect python-shell-interpreter(-args) when starting an interactive
session.

It also allows separate customization of the default Python command for
nonsessions and sessions.

This mainly benefits IPython users.  IPython isn't suitable as the
default command for nonsessions, but until now there isn't a way to set
it as the default interpreter for sessions only.

Another benefit is to promote greater consistency between ob-python.el
and upstream python.el, in particular for shells started with
run-python.  If a user configures python-shell-interpreter(-args), then
ob-python will respect those settings now.

As explained in the NEWS entry, this change should have no effect on
users who previously configured `org-babel-python-command', or on users
who stick to the default `python-shell-interpreter'.  But I submit the
patch for review before applying it, because it involves changing the
default values of some custom variables.

>From a49ddcb6ef72cfefab400e36e6d4a19e869c47a1 Mon Sep 17 00:00:00 2001
From: Jack Kamm <jackkamm@gmail.com>
Date: Fri, 29 Dec 2023 13:22:18 -0800
Subject: [PATCH] ob-python: Changed options for default Python command

ob-python will now use the same settings as `run-python' when starting
interactive sessions, by default.

* lisp/ob-python.el (org-babel-python-command): Changed to have
default value of nil.
(org-babel-python-command-session): New option to control default
session Python command.
(org-babel-python-command-nonsession): New option to control default
nonsession Python command.
(org-babel-execute:python): Set `org-babel-python-command-session' and
`org-babel-python-command-nonsession' using :python header arg.
(org-babel-python-initiate-session-by-key): Call `run-python' without
CMD arg.  Instead, set `python-shell-interpreter' and
`python-shell-interpreter-args' when needed.
(org-babel-python-evaluate-external-process): Use
`org-babel-python-command-nonsession' to start nonsession Python.
---
 etc/ORG-NEWS      | 30 ++++++++++++++++++++++++
 lisp/ob-python.el | 58 ++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 75 insertions(+), 13 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index c54473f55..688735a5b 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -551,6 +551,36 @@ Currently implemented options are:
 The capture template expansion element =%K= creates links using
 ~org-store-link~, which respects the values of ~org-id-link-to-use-id~.
 
+*** Changes to ~org-babel-python-command~, and new session/nonsession specific 
options
+
+The default Python command used by interactive sessions has been
+changed to match ~python-shell-interpreter~ and
+~python-shell-interpreter-args~ by default.  The default Python
+command for nonsessions has not changed.
+
+New options ~org-babel-python-command-nonsession~ and
+~org-babel-python-command-session~ control the default Python command
+for nonsessions and sessions, respectively.  By default,
+~org-babel-python-command-session~ is nil, which means to use the
+configuration for ~python-shell-interpreter(-args)~ as default.
+
+The old option ~org-babel-python-command~ has been changed to have
+default value of nil.  When non-nil, it overrides both
+~org-babel-python-command-nonsession~ and
+~org-babel-python-command-session~.  Therefore, users who had
+previously set ~org-babel-python-command~ will not experience any
+changes.
+
+Likewise, users who had neither set ~org-babel-python-command~ nor
+~python-shell-interpreter(-args)~ will not see any changes -- ~python~
+remains the default command.
+
+The main change will be for users who did not configure
+~org-babel-python-command~, but did configure
+~python-shell-interpreter~, e.g. to use IPython.  In this case,
+~ob-python~ will now start interactive sessions in a more consistent
+manner with ~run-python~.
+
 ** New features
 *** =ob-plantuml.el=: Support tikz file format output
 
diff --git a/lisp/ob-python.el b/lisp/ob-python.el
index 6b3a608c8..2b17f41fe 100644
--- a/lisp/ob-python.el
+++ b/lisp/ob-python.el
@@ -46,10 +46,31 @@ (defconst org-babel-header-args:python
     (python . :any))
   "Python-specific header arguments.")
 
-(defcustom org-babel-python-command "python"
-  "Name of the command for executing Python code."
-  :version "24.4"
-  :package-version '(Org . "8.0")
+(defcustom org-babel-python-command nil
+  "Name of the command for interactive and non-interactive Python code.
+If set, it overrides `org-babel-python-command-session' and
+`org-babel-python-command-nonsession'."
+  :version "29.2"
+  :package-version '(Org . "9.7")
+  :group 'org-babel
+  :type '(choice string (const nil)))
+
+(defcustom org-babel-python-command-session nil
+  "Name of the command for starting interactive Python sessions.
+If `nil' (the default), uses the values from
+`python-shell-interpreter' and `python-shell-interpreter-args'.
+If `org-babel-python-command' is set, then it overrides this
+option."
+  :version "29.2"
+  :package-version '(Org . "9.7")
+  :group 'org-babel
+  :type '(choice string (const nil)))
+
+(defcustom org-babel-python-command-nonsession "python"
+  "Name of the command for executing non-interactive Python code.
+If `org-babel-python-command' is set, then it overrides this option."
+  :version "29.2"
+  :package-version '(Org . "9.7")
   :group 'org-babel
   :type 'string)
 
@@ -70,9 +91,14 @@ (defcustom org-babel-python-None-to 'hline
 (defun org-babel-execute:python (body params)
   "Execute Python BODY according to PARAMS.
 This function is called by `org-babel-execute-src-block'."
-  (let* ((org-babel-python-command
+  (let* ((org-babel-python-command-nonsession
+         (or (cdr (assq :python params))
+             org-babel-python-command
+              org-babel-python-command-nonsession))
+         (org-babel-python-command-session
          (or (cdr (assq :python params))
-             org-babel-python-command))
+             org-babel-python-command
+              org-babel-python-command-session))
         (session (org-babel-python-initiate-session
                   (cdr (assq :session params))))
         (graphics-file (and (member "graphics" (assq :result-params params))
@@ -267,13 +293,20 @@ (defun org-babel-python-initiate-session-by-key 
(&optional session)
     (let* ((session (if session (intern session) :default))
            (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))
            (python-shell-buffer-name
            (org-babel-python-without-earmuffs py-buffer))
            (existing-session-p (comint-check-proc py-buffer)))
-      (run-python cmd)
+      (if org-babel-python-command-session
+          (let* ((cmd-split (split-string-and-unquote
+                             org-babel-python-command-session))
+                 (python-shell-interpreter (car cmd-split))
+                 (python-shell-interpreter-args
+                  (append (cdr cmd-split)
+                          (when (member system-type
+                                        '(cygwin windows-nt ms-dos))
+                            (list "-i")))))
+            (run-python))
+        (run-python))
       (with-current-buffer py-buffer
         (if existing-session-p
             ;; Session was created outside Org.  Assume first prompt
@@ -374,7 +407,7 @@ (defun org-babel-python-evaluate-external-process
 non-nil, then save graphical results to that file instead."
   (let ((raw
          (pcase result-type
-           (`output (org-babel-eval org-babel-python-command
+           (`output (org-babel-eval org-babel-python-command-nonsession
                                    (concat preamble (and preamble "\n")
                                             (if graphics-file
                                                 (format 
org-babel-python--output-graphics-wrapper
@@ -382,8 +415,7 @@ (defun org-babel-python-evaluate-external-process
                                               body))))
            (`value (let ((results-file (or graphics-file
                                           (org-babel-temp-file "python-"))))
-                    (org-babel-eval
-                     org-babel-python-command
+                    (org-babel-eval org-babel-python-command-nonsession
                      (concat
                       preamble (and preamble "\n")
                       (format
-- 
2.43.0