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:

#!/usr/bin/env python3

def a():
    print("a")

def b():
    print("b")

def c():
   print("c")

b()
a()

if __name__ == "__main__":
    main()

(Also, why is there an extra blank line before the incorrectly
indented block?)

Is this user error on my part somehow? I suppose I could write my own
version of tangle, though I’m not clear if the whitespace is lost in
the tangle function or in the Org mode data model.

Thoughts?

                                        Be seeing you,
                                          norm

--
Norman Walsh <ndw@nwalsh.com> | We discover in ourselves what others
http://nwalsh.com/            | hide from us, and we recognize in
                              | others what we hide from
                              | ourselves.--Vauvenargues