# [Doc-SIG] Last Friday, "groups", washing machines

Tony J Ibbs (Tibs) tony@lsl.co.uk
Mon, 19 Nov 2001 11:16:18 -0000

Humph. OK, Friday happened, and we have a new washing machine, but for
reasons mostly to do with the vagaries of how such things get delivered
and the difficulties of arranging childcare and pickup around them, I
actually got less than two hours of computer time - and essentially none
over the weekend for other reasons. Mind you, we're now building up a
nice backlog of ironing, so it's not all downside!

I managed to write something on <group> and "style", but it's still a
bit hazy, and I haven't had time to make it shorter. Still, rather than
put it off, here goes:

.. begin:: reST included text
.. ############################################################

Adding <group>, losing <package_section> and their ilk
======================================================

:Author: Tibs
:Date: 2001-11-18

Background
----------
I am currently writing software that will take information from
Python source files, produce a DPS node tree therefrom, and allow
the user to generate HTML from that.

My initial implementation produced a *variant* of the DPS node
tree, which contained many structures that related closely to the
information derived from Python - for instance, something like::

<py_class name="Fred">
<docstring>
This is a very silly class.
<py_attr_list>
<py_attr name="jim">
<py_method "name="method">

For various reasons, the (implicit) DTD wasn't shaping up very
possibility of amending the "standard" DTD. This led to a
discussion of how the flow of information through a DPS processor
should actually work, with the result being David's diagram
[#diagram]_::

+--------+     +--------+     +------------+     +--------+
| READER | --> | linker | --> | transforms | --> | WRITER |
+--------+     +--------+     +------------+     +--------+
|                          TOC, index,            |
|                          etc. (optional)        |
+--------+                                       +--------+
| PARSER |                                       | filer  |
+--------+                                       +--------+

David also made the point that, within this plan, the result of
the linker phase is a normal DPS tree, which can be
transformed with any of the "standard" transformation tools (for
instance, to resolve automatic footnotes), and then output with
any writer.

Whilst David's diagram is not *quite* how I see the process, it's
close enough for this purpose. Thus pydps [#pydps]_ might be shown
as::

+--------+     +--------------+     +------------+     +---------+
| READER | --> | transform.py | --> | transforms | --> | html.py |
+--------+     +--------------+     +------------+     +---------+
|                                                      |
+----------+                                     +---------------+
| visit.py |                                     | buildhtml.py  |
+----------+                                     +---------------+

The "READER" is implicit in the main utility (currently
pydps.py), and locates the relevant Python files. It then
uses visit.py to generate a tree representing the Python code
(the Python compiler module, standard with Python 2.2 and
above, but in Tools before that, is used).

transform.py (which, by David's diagrams, should maybe be
called link) transforms that information into a proper DPS
node tree. At the time of writing, no transformations are done.

Finally, HTML is output from the DPS node tree by html.py.

So, in summary:

1. transform.py generates a *normal* DPS tree. It doesn't
use any "odd" nodes (except <group> - but we'll discuss
that later on). This means that it should be possible to
plug in any other writer, and produce a different format as
output - a very significant advantage.

2. html.py expects to be given a *normal* DPS tree. This
means that it should be usable by any other utility that
also provides a normal DPS tree - again an advantage.

The problem
-----------
But there is a clash in requirements here. Whilst it is very nice
to be able to represent the Python information as "normal" DPS
(guaranteeing that anyone can do useful things with it), there is
some need to transfer information that goes beyond that. There
are two main reasons for wanting to do this:

* Data mining
* Presentation

For the first, although DPS/reST/pydps is primarily about
producing human-viewable documentation, it might also be nice to
be able to extract parts of it automatically, for various
purposes - for instance, retrieve just the information about
which classes inherit from other. This information will, in part,
be obvious from the text chosen within the document (a title like
"Class Fred" might be taken to be useful, for instance!), but it
would be nice to give a bit more help.

For the second, it's relatively difficult to produce better
work on. If one uses the (rather garish) default presentation
produced by pydps (and no, I'm not saying that's a *nice*
presentation, but it is the one I've got as an example), it is
clearly useful to be able to:

1. group together the package/class/method/etc title and its
full name/path/whatever

2. group together a method or function's signature and its
docstring

David's original approach to this was to introduce a host of
Python specific tags into nodes.py [#nodes]_ - for instance::

package_section
module_section
...
instance_attribute_section
...
parameter_item
parameter_tuple
...
package
module
class_attribute

There are several problems with approach. Perhaps the most
serious is that *all* generic DPS writers need to understand
this host of elements that are only relevant to Python. Clearly,
someone writing a writer for other purposes may be reluctant to
go to this (to them) redundant effort.

>From my point of view, an immediate problem is that the set of
elements is not *quite* what I want - which means working towards
a set of patches for nodes.py and the relevant DTD, and
getting David to agree to them (well, that last is a useful
process to have in place, but still). Since I'm not likely to get
it right immediately, this is a repetitive process.

Lastly, one might imagine someone from another programming
language domain adopting DPS/reST. One can expect them to be
frustrated if the set of constructs provided for Python doesn't
quite match the set of constructs required to describe their
language in a natural manner.

Luckily (!), I have a counter proposal, which hopefully keeps the
baby and just loses the bath water.

Groups and "style"
------------------
The first thing that I realised was that, for convenience of
output at least, I wanted to be able to group elements together -
or, in terms of the DPS tree, insert an arbitrary "subroot"
within the tree to 'abstract' a branch of the tree.

This is particularly useful for linking together the parts of the
text that deal with (for instance) attribution, or unusual
globals, without having to embed yet another section.

There is, of course, precedent. HTML provides <div> and <span> -
one for "structural" elements, and one for inline elements (I
forget which is which), and TeX and LaTeX are well-known for
their use of grouping (e.g., the \begin{xxx} and
\end{xxx} in LaTeX).

I don't consider it worth making the <div>/<span> distinction in
the context of a tree - it is perfectly evident what is beingp
grouped from the elements themselves.

Once one has a <group> element, it is natural to annotate it with
*what* it is a group of/for. I chose the arbitrary term "style" -
partly because it is not used in HTML/XML for any purpose I am
aware of.

And once one has the "style" attribute, it becomes possible to
use it elsewhere - most notably in <section> elements, saving the
need for a myriad of different sections for different purposes.

In these instances, it is perhaps acting more like the "class"
attribute in HTML - indicating, to some extent, meaning, but
aimed mostly at presentation (via CSS).

The other obvious place to use it is in the automatically
generated text for things like names, where (at least
pre-"combing"/transformation) one is "pretending" to have
assigned a role (just as a person might in a docstring) (but see
[#style]_).

Summary
-------
Current DPS defines many element types for use in Python code
representation.

However, there are major advantages in only using the "simple"
DPS nodes for all purposes.

This becomes simple and practical given a single extra, general
purpose, element: <group>.

Furthermore, adding a standard attribute called "style" (or
perhaps "role" - see [#style]_) seems to fulfil any other
outstanding requirements.

References
----------
.. [#diagram] in email by David Goodger to Doc-SIG, dated
21 September 2001 04:31, "Re: [Doc-SIG] DPS components".

.. [#style] Hmm - maybe "style" should be "role", to match
with the way that a :role:of something gets handled...

.. [#pydps] Normally to be found at
http://www.tibsnjoan.co.uk/reST/pydps.tgz,
although note that this is not currently up-to-date.

.. [#nodes] dps/dps/nodes.py in the DPS distribution
(dps.nodes if one is importing it).

.. ############################################################
.. end:: reST included text

Tibs

--
Tony J Ibbs (Tibs)      http://www.tibsnjoan.co.uk/
"No one trike will do everything... buy the whole set!" - Rob Hague
My views! Mine! Mine! (Unless Laser-Scan ask nicely to borrow them.)