code: def set_range_value(self, data):
          
          dtfrom = data.pop('value_from')
          dtto = data.pop('value_to')
          if dtfrom is dtto is None:
              self.errors['value'] = ['Date range requires values']
              raise forms.ValidationError([])
          data['value'] = (dtfrom, dtto)
docs: Validates date range by parsing into 2 datetime objects and
          validating them both.