| from django.db import models | |
| from django.utils import timezone | |
| def expensive_calculation(): | |
| expensive_calculation.num_runs += 1 | |
| return timezone.now() | |
| class Poll(models.Model): | |
| question = models.CharField(max_length=200) | |
| answer = models.CharField(max_length=200) | |
| pub_date = models.DateTimeField( | |
| 'date published', default=expensive_calculation | |
| ) | |