The Spyder docs list other implementations of the percent format for notebooks as markdown and for delimiting runnable blocks within source code:

  # %%

  "^# %%"

Org-mode was released in 2003: https://en.wikipedia.org/wiki/Org-mode

Org-mode supports code blocks: https://orgmode.org/manual/Structure-of-Code-Blocks.html :

  #+BEGIN_SRC <language> and 
  #+END_SRC. 

Literate programming; LaTeX: https://en.wikipedia.org/wiki/Literate_programming

Notebook interface; Markdown + MathTeX: https://en.wikipedia.org/wiki/Notebook_interface ;

  $ \delta_{2 3 4} = 5 $

  $$ \Delta_\text{3 4 5} = 56 $$