On 13 November 2001, Jeff Rush said:
> Is there an example of forms/widget usage anywhere?  I've
> wrestled with the source code and can't get it to do
> anything but response 500.

Try the attached -- this is one of the PTL modules from SPLAT!, a bug
database I wrote to 1) showcase Quixote, 2) play with/learn about
Berkeley DB, and 3) track the MEMS Exchange's bugs.  So far #2 and #3
are goiing swimmingly, but I have yet to release SPLAT!, so #1 is not
quite there yet.  Sigh.

Here's how it works:

  * _q_index() generates the bug index page, URL "/bugs"

  * two of the links from the bug index page are "/bugs/display"
    and "/bugs/filter", implemented by the display() and filter()
    templates in this module

  * display() calls gen_display_widgets() to create the widgets used
    in a form that allows the user to customize the bug index
    by changing how bugs are sorted and grouped.  Those widgets
    are saved in the session object, because we're going to need
    them again when we process the form.

  * display() then creates a form, where much of the HTML is
    generated by calling 'render()' on the various widget
    objects created by gen_display_widgets()

  * the form is handled by the "/bugs/set_display" URL, implemented
    by the set_display() template.  First thing it does is pull the
    widgets out of the session object, and then it calls parse() on
    each widget to get the widget value out.  Then it tells the
    SPLAT! Preferences object the user's preferences (taken from
    the form value); this is used by _q_index(), next time we
    generate the bug index page.

  * finally, set_display() redirects to "/bugs" (URL_PREFIX), to
    show a new (differently sorted/group) bug index

filter()/gen_filter_widgets()/set_filter() work similarly.

There is certainly more than one way to do it; there are various minor
weaknesses in this scheme, which I leave as an exercise to the reader to
work out.  (Hint: what happens if you try to access "/bugs/set_display"
in a brand-new SPLAT! session?)

Also, this doesn't use the Form class at all, because 1) I wanted to
experiment with the Widgets on their own, and 2) I think Form is
overkill here.  I could be wrong; Form buys you a hell of a lot of
useful stuff.  The Widget class hierarchy does too.  Together, they're a
very powerful and useful combination.

> The traceback complains about
> a call to set_body(output) where output is not a string
> and not a None either.  Odd.

I don't recall seeing that.  If you keep getting it, please supply a
full traceback.  And if you figure out what you were doing wrong that
caused such an obscure error, let us know; we'll try to make the error
more obvious.  (That's assuming this is your mistake... you might well
have hit a bug!)

        Greg
--
Greg Ward - software developer                gward@mems-exchange.org
MEMS Exchange                            http://www.mems-exchange.org