[Zope] DateTime under phyton script

Hi! I have a form. It contains 3 drop-down boxes, named start_year:int, start_month:int, start_day:int. How can I use them, to make a datum object under phyton script? I try starttime = DateTime(container.REQUEST.start_year, container.REQUEST.start_month, container.REQUEST.start_day) but it gives an error Error Type: TypeError Error Value: illegal argument type for built-in operation Could anybody help me? Thanks: Lajos Kerekes