If I understand what you are asking then Python & CGI are a poor solution. It would be easy to have one page ask for the month, click submit, then have a second page ask for the exact date. Easy; but terrible design.
You want to have one page with a dropdown of months. When you select a month, you want to dynamicly alter a dropdown of dates without refreshing the page. For this task you'll want to pull JavaScript out of your toolbox. This is a fairly common "problem" and googling for examples/samples should be quick-n-easy. -- http://mail.python.org/mailman/listinfo/python-list
