from robokassa.forms import RobokassaForm
    form = RobokassaForm(initial={
        'OutSum': price,
        'InvId': order_id,
        'Culture': 'ru'
    })

    def _get_signature_string(self):
        def _val(name):
            value = self.initial[name] if name in self.initial else self.fields[name].initial
            if value is None:
                return ''
            return unicode(value)
        standard_part = ':'.join([_val('MrchLogin'), _val('OutSum'), _val('InvId'), PASSWORD1])
        return self._append_extra_part(standard_part, _val)

    def _get_signature(self):
        return md5(self._get_signature_string()).hexdigest().upper()