@property
    def amazon_url(self):
        if self.isbn:
            try:
                return 'http://www.amazon.com/dp/%s/?%s' % (self.isbn, settings.AMAZON_AFFILIATE_EXTENTION)
            except:
                return self.isbn % 'http://www.amazon.com/dp/%s/'
        return ''
dataset/ETHPy150Open nathanborror/django-basic-apps/basic/books/models.py/Book.amazon_url/swapped operands of `%`