Custom Filter in Django Admin on Django 1.3 or below

How can I add a custom filter to django admin (the filters that appear on the right side of a model dashboard)? I know its easy to include a filter based on a field of that model, but what about a "calculated" field like this: class NewsItem(models.Model): headline = models.CharField(max_length=4096, blank=False) byline_1 = models.CharField(max_length=4096, blank=True) dateline = models.DateTimeFi

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admin filter custom