django日期比较

from django.db import models
from django.utils import timezone
import datetime

# Create your models here.
class Question(models.Model):
    question_text=models.CharField(max_length=200)
    pub_date=models.DateTimeField('date published')
    def __str__(self):              # __unicode__ on Python 2
        return self.question_text
    def was_published_recently(self):
        # return self.pub_date >= timezone.now()- datetime.timedelta(days=1)
        if self.pub_date >= timezone.now()- datetime.timedelta(days=3):
            return 'new'
        else:
            return 'old'