Picky, Skin, SaxLifter
Found some time to continue work on the Picky Picky Game. I have something which, given a graphics file, writes it in to the correct place in the directory structure. Tonight’s task was a routine for generating the index page, based on the pictures stored so far. In the eventual web application, this routine will be invoked in CGI scripts whenever a new picture is added or vote recorded. For the present I can just run the Python script (one of the ways in which creating web apps in Python is less hassle than, say, ASP .Net or webclasses).
The index page format is mainly controlled through a
‘skin’ file index.skin. This has most
of the HTML, with special XML tags for interpolating the dynamic
content. This way hopefully Jeremy will be able to hack the
HTML without touching any of the application code. (The
immediate inspiration for the term skin comes from the
Helma Object Publisher system,
which does something similar, but using JavaScript.)
The picture metadata is written in XML which is straightforward
enough except that Python’s native
SAX support is broken:
it does not support XML namespaces! I have fixed this
with my own SAX filter
dubbed SaxLifter: it processes
startElement events by scanning the attributes for
namespace prefixes, maintaining a stack of namespace mappings,
and generating startElementNS events. Presumably
if I were using the XML-SIG or 4Thought enhancements to
Python things would work better. Sigh.
The overall strategy is to generate as much static HTML as possible—that is, instead of creating the HTML for the list of pictures afresh each time someone visits the site (which is what PHP and ASP, etc., do), I intend to generate it only when a new picture is added to the list. Since adding pictures will happen much more rarely than viewing the list, this reduces the overall load on the web server. The aim is to use CGI only in the pages that make a change (adding a picture or voting).