Add tools to "whiten" some output of Black

README.org

@@ -4623,6 +4623,8 @@ configuration:
    modes and proper directory local variables (meaning in presence of a proper
    file [[info:emacs#Directory Variables][.dir-locals.el]] in the root directory of any project using proper
    programming modes).
+4. Listing [[lst:whiten-black]] defines Emacs Lisp functions to undo (whiten) some
+   output of [[https://black.readthedocs.io/en/stable/][Black]] after src_emacs-lisp{(org-babel-tangle)}.
 
 #+caption[Ensure =eglot= installation with minimal setup]:
 #+caption: Ensure =eglot= installation with minimal setup.
@@ -4752,6 +4754,52 @@ This is to advice `org-edit-src-exit' and `org-edit-src-save'."
   (add-hook 'after-change-major-mode-hook #'eglot-maybe-ensure))
 #+end_src
 
+#+caption[Whiten Black]:
+#+caption: Whiten Black
+#+name: lst:whiten-black
+#+begin_src emacs-lisp -n
+(with-eval-after-load 'emacs
+  (defun black-python-sequence ()
+    "Try to find a Blackened Python sequence to whiten."
+    (interactive)
+    (if (derived-mode-p 'python-mode)
+        (re-search-forward "[[(][ \t]*$" nil t)
+      (org-narrow-to-block)
+      (re-search-forward "[[(][ \t]*$" nil t)
+      (widen)))
+
+  (defun whiten--python-sequence ()
+    "Whiten a Blackened Python sequence without narrowing.
+Call `widen' after an `user-error'."
+    (if (not (and (looking-at-p "[ \t]*$")))
+        (user-error "Call `widen': not seeing `new-line'")
+      (skip-chars-backward " \t\\[\\(")
+      (if (not (looking-at-p "[ \t]*[[(][ \t]*$"))
+          (user-error "Call `widen': not seeing `[' or `(' before `new-line'")
+        (fixup-whitespace)
+        (skip-chars-forward " \\[\\(")
+        (kill-line)
+        (fixup-whitespace)
+        (move-end-of-line 1)
+        (while (and (eq ?\, (char-before)))
+          (kill-line)
+          (fixup-whitespace)
+          (move-end-of-line 1))
+        (save-excursion
+          (when (memq (char-before) '(?\) ?\]))
+            (goto-char (1- (point)))
+            (delete-char -1))))))
+
+  (defun whiten-python-sequence ()
+    "Whiten a Blackened Python sequence.  Call `widen' after an `user-error'."
+    (interactive)
+    (if (derived-mode-p 'python-mode)
+        (whiten--python-sequences)
+      (org-narrow-to-block)
+      (whiten--python-sequence)
+      (widen))))
+#+end_src
+
 #+caption: Real sessions for ~eval-buffer~ in ~org-src~ buffers.
 #+begin_src org -n :tangle eval-buffer-in-org-src-buffers.org
 ,#+title:  Sessions for ~eval-buffer~ in ~org-src~ buffers