[Zope] self-referential page design

[Jeff Sacksteder]

I'm looking for general advice on how I can have a page that contains a
search interface AND the results of that search. A detailed description
follows.

I have page which displays summarized business information for the current
month. It is composed of tables which describe the general layout, and each
cell contains the results of various other dtml documents generated from
zsql queries. 

I want to add a drop-down form to select the month you would like to view
the information from. This I can do; let's call the field in the form
input_month. Once I have the page loaded, I can select the month to view and
all the component parts run their queries using the input_month parameter.
Great. However, when I load the root document, input_month does not have an
assigned value. By default , I want it to display the current month. I can
derive that information with python script magic. What would be the best way
to assign a value to that variable if it's current value is null? I have
some ideas, but most of them are bad.