class PlNipField(models.CharField):
    def __init__(self, *args, **kwargs):
        verbose_name = kwargs.pop('verbose_name', _("numer identyfikacji podatkowej"))
        max_length = kwargs.pop('max_length', 13)
        super(PlNipField, self).__init__(verbose_name=verbose_name, max_length=max_length, *args, **kwargs)