我正在尝试将Django项目从Python 2.7 / Django 1.11迁移到Python 3.7 / Django 2.1。

我发现了一个问题，我想了解其原因。

我的项目中有3个模型：

class DeviceModel(models.Model):
    name = models.CharField(max_length=255)
    pirsh = models.CharField(max_length=255)

    def __str__(self):
        return self.name + " - " + self.pirsh

class Device(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    device_model = models.ForeignKey(DeviceModel, on_delete=models.CASCADE)
    serial_number = models.CharField(max_length=255)


    def __str__(self):
        return self.device_model.name + " - " + self.device_model.pirsh + " - " \
                + self.serial_number

class DeviceTest(models.Model):
    device = models.ForeignKey(Device, on_delete=models.CASCADE)
    created_at = models.DateTimeField()

    TEST_OK = '+'
    TEST_ERROR = '-'
    TEST_PENDING = '?'
    TEST_RESULT_CHOICES = (
        (TEST_OK, 'Success'),
        (TEST_ERROR, 'Fail'),
        (TEST_PENDING, 'Not checked'),
    )
    status = models.CharField(max_length=1, choices=TEST_RESULT_CHOICES, default=TEST_PENDING)

    comment = models.TextField(blank=True, default="")
    tester = models.CharField(max_length=255)
    action = models.CharField(max_length=255)

    def save(self, *args, **kwargs):
        ''' On save, update timestamps '''
        if not self.created_at:
            self.created_at = timezone.now()
        return super(DeviceTest, self).save(*args, **kwargs)

    def __str__(self):
        return  self.device_id.device_model.name + " - " + \
                self.device_id.device_model.pirsh + " - " + \
                self.device_id.serial_number + " - " + \
                str(self.created_at) + " - " + \
                "Result (" + self.status + ")"

这是我的代码，用于Device按最新测试状态对对象进行排序（从GET请求中解析“ dev_filter”，“ field”和“ order”参数）：

if (dev_filter!="") and (dev_filter!="-1"):
    device_list = Device.objects.all().filter(device_model = dev_filter)
else:
    device_list = Device.objects.all()

dev_status_list = []
for dev in device_list:
    try:
        dev_status_list.append(DeviceTest.objects.filter(device_id=dev.pk).latest('created_at').status)
    except:
        dev_status_list.append("Not checked")

device_list = [device_list for (dev_status_list, device_list) in sorted(zip(dev_status_list, device_list))]

if (order == '-'):
    device_list.reverse()

这段代码在Python 2.7 / Django 1.11中工作正常，但在Python 3.7 / Django 2.1中却没有

Django将其标记为错误sorted(zip(dev_status_list, device_list))功能：

TypeError: '<' not supported between instances of 'Device' and 'Device'

我看到了针对此问题的两种解决方案：

device_list = [device_list for (dev_status_list, device_list) in sorted(zip(dev_status_list, device_list), key=lambda x: (x[0],x[1].__str__()))]

或添加__lt__方法进行Device建模：

def __lt__(self, other):
    return self.__str__() < other.__str__()

我的问题是-发生了什么变化？是否由于Python升级或Django升级而发生此错误？Python 2.7 / Django
1.11框架中Device对象的默认排序方法是什么？我是否正确，它是字符串表示形式？而我的哪种解决方案是首选？