Re: “Literate” python?

["Berry, Charles" <ccberry@health.ucsd.edu>]

> On Nov 29, 2019, at 9:54 AM, Norman Walsh <ndw@nwalsh.com> wrote:
> 
> Hi,
> 
> I’ve seen a couple of pointers recently to using Org mode and tangle
> to write more literate Emacs configurations. I use Org+babel all the
> time to write “interactive” documents, so I thought I’d try out tangle
> from Org.
> 
> I didn’t want to start with something as comlicated as my Emacs
> config :-) so I figured I’d kick the tires with a small python
> program. That did not end well.
> 
> Consider:
> 
> #+TITLE: Python literate programming
> #+OPTIONS: html-postamble:nil
> 
> It starts off as a completely standard Python3 program.
> 
> ---%<------------------------------------------------------
> #+BEGIN_SRC python :tangle yes :weave no
> #!/usr/bin/env python3
> 
> #+END_SRC
> 
> It defines ~a~.
> 
> #+BEGIN_SRC python :tangle yes
> def a():
>    print("a")
> 
> 
> #+END_SRC
> 
> And ~b~.
> 
> #+BEGIN_SRC python :tangle yes
> def b():
>    print("b")
> 
> 
> #+END_SRC
> 
> Now ~c~ is a little more complicated:
> 
> #+BEGIN_SRC python :tangle yes
> def c():
>   print("c")
> #+END_SRC
> 
> Not only does ~c~ print “c”, it calls ~a()~ and ~b()~.
> 
> #+BEGIN_SRC python :tangle yes
>   b()
>   a()
> #+END_SRC
> 
> Finally, make it importable. Not that you’d want to.
> 
> #+BEGIN_SRC python :tangle yes
> if __name__ == "__main__":
>    main()
> #+END_SRC
> --->%------------------------------------------------------
> 
> That’s the script. It weaves into HTML more-or-less ok (there’s a
> weird black box at the front of indented lines, but I can come back to
> that later).
> 
> It’s a complete mess when tangled.
> 
> The extra blank lines between functions (to make pylint happy with
> some PEP guideline) have disappeared. I guess I could live with that,
> but the complete failure to preserve indention in the penultimate code
> block is a show stopper:

[results of tangling deleted]

A couple of things might help.

First, use the :noweb-ref argument to mark each of the code blocks you wish to tangle.  

Say `:noweb-ref tangleyes'. Or some more evocative name.

Remove the `:tangle yes' from each of those. Then, add a code block that has only `<<tangleyes>>' in it and tangle it.

#+begin_src python :noweb yes :tangle yes
<<tangleyes>>
#+end_src

The remaining problem (as you will see) is the indentation. Fix this by adding the `-i' flag to the penultimate code block, viz.

#+BEGIN_SRC python -i :noweb-ref tangleyes
   b()
   a()
#+END_SRC

See 12.6 Literal Examples and 15.10 Noweb Reference Syntax in the manual.

HTH,

Chuck