如何定义Django模型方法?

Models.py

    class Amazoninv(models.Model):
       SKU = models.IntegerField()
       Description = models.CharField(max_length=300)
       BanggoodID = models.IntegerField()
       Website = models.CharField(max_length = 250)
       StockInfo = models.CharField(max_length = 200)
       Qty = models.IntegerField()
       Cost = models.IntegerField()
       promotion_enddate = models.DateTimeField(null=True, blank=True)
       reorder = models.IntegerField()

    def __str__(self):
       return self.Description

当我在django admin中查看时,它只将对象显示为Amazoninv object(1),Amazoninv object(2)。它没有在Amazoninv def中显示描述。我们需要安装(pip)任何东西才能在django中运行方法吗?