Re: Re: Babel, Python and UTF-8

["Eric Schulte" <schulte.eric@gmail.com>]

Vincent Beffara <vbeffara@ens-lyon.fr> writes:

> Hi,
>
>>> (and it would be excellent to allow for a code block as a preamble,
>>> instead of a string in the header or as an alternative, because
>>> preambles once they are allowed tend to grow uncontrollably ;->)
>>
>> This is currently possible using the `sbe' function.  Arbitrary emacs
>> lisp can be placed inside of header arguments, and the `sbe' take the
>> name of a code block and returns its result.
>
> Very cool ! That does all I want, thanks for the info. For multi-line it
> is a bit heavy to write, with lots of \n and preamble .= "lskjd", but I
> can live with that. Unless there is a way already to write something
> like this ?
>
> #+source: my-preamble
> #+begin_src python :return preamble
>   # -*- coding: utf-8 -*-"
>   import os,sys,whatever
> #+end_src
>
> #+begin_src python :preamble (org-babel-get-and-expand-source-code-body my-preamble) :return s
>   s = "é"
> #+end_src
>
> There is org-babel-get-src-block-info but it looks at the block around
> (point), not by name ... so I guess it would not be too hard to write
> the extraction method, but it might be somewhere in the code already.
>

Yes, the following uses an internal Babel function, but is probably much
simpler

#+results: my-preamble
: # -*- coding: utf-8 -*-
: import os,sys,whatever

#+begin_src python :preamble (org-babel-ref-resolve "my-preamble") :return s
s = "é"
#+end_src

Note that as written this will return the following python error

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ImportError: No module named whatever

>
>>> One naive question : why is the code path different for tangling and
>>> evaluation ? One would think that a natural way for evaluation would be
>>> to tangle the current block (plus included noweb stuff etc) into a
>>> temporary file and eval that file ... and that would enable shebang for
>>> evaluation as well. There must be something I am missing here.
>>
>> Tangling works for *any* programming language, even those which have yet
>> to be created and have no explicit Emacs or Org-mode support, this is
>> because on tangling the code block is simply treated as text.
>
> As far as I understood from testing, tangling does adapt to the language
> (at least to implement :var in a suitable way), so I was under the
> impression that evaluating could be implemented as some kind of wrapping
> around the tangled output - and obviously the wrapping would have to be
> language-specific even if for the most part the tanglong is not.
>

Yes, some language specific features (e.g. variable expansion) can be
used by the tangling mechanisms if such features are defined for the
language in question, however tangling can be done in the absence of any
language specific features and thus works for any arbitrary language.

That shebang and preamble should remain separate for the other reasons
mentioned in my previous email.

>
> I am just discovering all of this, sorry if I have horrible
> misconceptions about the thing ...
>

No problem, it is a fairly (but I don't think overly) complex system.

>
> Regards,
>
>         /v
>
>
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