code: def require(self, fieldname, allow_blank=False):
          
          if self.request.form and fieldname not in self.request.form.keys():
              raise Exception("Required field not found in request: %s" % fieldname)
          if self.request.form and (not self.request.form[fieldname] or allow_blank):
              raise Exception("Required field %s may not have blank value")
docs: fieldname is required