Re: Babel: communicating irregular data to R source-code block

[Eric Schulte <eric.schulte@gmx.com>]

[...]
>
> I'm beginning to see why you have strong feelings about python.

Semantically meaningful whitespace is a bad idea for a programming
langauge.

> In the code above, the blank line before #+end_src is necessary and
> must not contain any spaces, and :var n can be set to anything, since
> it is declared for initialization only.
>
> The code in the JSS article doesn't run for me with a recent Org-mode
> unless I add a blank line before #+end_src, or remove the :return header
> argument.  If I remove the :return header argument, then the need for
> the blank line goes away.  The following code block seems to work:
>
> #+name: pascals-triangle
> #+begin_src python :var n=2 :exports none
> def pascals_triangle(n):
>     if n == 0:
>         return [[1]]
>     prev_triangle = pascals_triangle(n-1)
>     prev_row = prev_triangle[n-1]
>     this_row = map(sum, zip([0] + prev_row, prev_row + [0]))
>     return prev_triangle + [this_row]
> return pascals_triangle(n)
> #+end_src
>
> #+RESULTS: pascals-triangle
>
> | 1 |   |   |
> | 1 | 1 |   |
> | 1 | 2 | 1 |
>
> I'm guessing that the need for a blank line when using :results has
> arisen since the JSS article was published, because the article was
> generated from source code and didn't show any errors.  
>

I believe that we used to pad code blocks with newlines when they were
extracted from the buffer, which had the effect of automatically adding
this extra line.  This behavior however caused problems in some cases
where the extra line was not desired.

>
> If I have this right (a big if), then might it be possible to
> re-establish the old behavior so the JSS code works?  
>

I've just pushed up a patch in which the addition of the return value in
python is careful to add this newline itself.  This should restore the
functionality of the python code from the paper (specifically the
following now works [1]).  This is applied to the maint branch so
hopefully it will sync with Emacs before the release of Emacs24.

Best,


Footnotes: 
[1]  

#+name: pascals-triangle
#+begin_src python :var n=2 :exports none :return pascals_triangle(n)
def pascals_triangle(n):
    if n == 0:
        return [[1]]
    prev_triangle = pascals_triangle(n-1)
    prev_row = prev_triangle[n-1]
    this_row = map(sum, zip([0] + prev_row, prev_row + [0]))
    return prev_triangle + [this_row]
#+end_src

#+RESULTS: pascals-triangle

| 1 |   |   |
| 1 | 1 |   |
| 1 | 2 | 1 |


-- 
Eric Schulte
http://cs.unm.edu/~eschulte/