使用Freezegun冻结时区感知datetime仍触发RuntimeWarning的解决方法

问题场景 #

你在开发机构暂停功能的测试用例时，使用freezegun冻结了带UTC时区的datetime.datetime对象，打印验证时能看到时区感知的时间（2000-01-01 00:00:00+00:00），但运行测试时一直收到Django的RuntimeWarning：

/usr/local/lib/python2.7/dist-packages/django/db/models/fields/init.py:1447: RuntimeWarning: DateTimeField Organization.suspended received a naive datetime (2000-01-01 00:00:00) while time zone support is active. RuntimeWarning)

你的测试代码如下：

import datetime
import pytz
from freezegun import freeze_time
# crop
class OrganizationSuspendTestCase(TestCase):
    def setUp(self):
        self.organization = OrganizationFactory()
        self.fake_datetime = datetime.datetime(2000, 1, 1, 0, 0, 0, tzinfo=pytz.UTC)
        print self.fake_datetime
    def test_suspend_organization(self):
        """
        Case: An organization is being suspended with the suspend service.
        Expected: The organization is updated with the suspending datetime and the reason.
        """
        with freeze_time(self.fake_datetime):
            mc_organization.services.organization.suspend(organization=self.organization, reason="Did not pay the bill")
        self.assertEqual(self.organization.suspended, datetime.datetime(2000, 1, 1, 0, 0, 0))

问题根源 #

其实问题出在业务服务代码而非测试代码：你的测试用例正确冻结了带时区的时间，但服务内部原本使用datetime.datetime.now()生成的是无时区感知（naive）的时间对象——哪怕freezegun冻结了时间，datetime.datetime.now()返回的依然是不带时区的结果，而Django开启时区支持后，不允许将naive时间存入DateTimeField，因此触发了警告。

解决方案 #

将服务代码中获取当前时间的方式替换为Django提供的timezone.now()，这个方法会返回时区感知的时间对象，能和freezegun冻结的带时区时间兼容。修改后的服务代码如下：

def suspend(organization, reason):
    """
    Suspend an organization with the given reason.
    :param mc_organization.models.Organization organization: The organization to suspend.
    :param string reason: The reason of the suspending.
    :return: None
    """
    # organization.suspended = datetime.datetime.now() (Old situation)
    organization.suspended = timezone.now() # timezone aware situation.
    organization.suspended_reason = reason
    organization.save()

另外建议同步调整测试中的断言，使用带时区的时间对象，保持代码一致性：

self.assertEqual(self.organization.suspended, datetime.datetime(2000, 1, 1, 0, 0, 0, tzinfo=pytz.UTC))

内容的提问来源于stack exchange，提问作者Nrzonline