From the Django docs: http://docs.djangoproject.com/en/dev/ref/models/fields/#choices

Finally, note that choices can be any iterable object — not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you’re probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn’t change much, if ever.

Django >= 5

More options for declaring field choices

Django 5.0 adds support for accepting a mapping or a callable instead of an iterable, and also no longer requires .choices to be used directly to expand enumeration types:

def get_scores():
    return [(i, str(i)) for i in range(10)]


class Winner(models.Model):
    name = models.CharField(...)
    medal = models.CharField(..., choices=Medal)  # Using `.choices` not required.
    sport = models.CharField(..., choices=SPORT_CHOICES)
    score = models.IntegerField(choices=get_scores)  # A callable is allowed.

Previous versions

This is my approach:

I use lazy for lazy load:

from django.utils.functional import lazy

Here, a helper to chose options:

def help_SHOP_CHOICES():
    SHOP1_CHOICES = [
        ('Food Court', 'Food Court'),
        ('KFC', 'KFC'),
      ]
    SHOP3_CHOICES = [
        ('Bowling Arena', 'Bowling Arena'),
        ('Cinemax', 'Cinemax'),
      ]
    return random.choice( SHOP1_CHOICES + SHOP3_CHOICES )   # choose one

Finally the model with dynamic choices:

class Feed(models.Model):
  ...
  location=models.CharField(max_length=25, choices=SHOP1_CHOICES)

  def __init__(self, *args, **kwargs):
     super(Feed, self).__init__(*args, **kwargs)
     self._meta.get_field('location').choices = \
                        lazy(help_SHOP_CHOICES,list)()

I don’t think you should do this on the model, form is a better place. Or you should rethink your models. For example:

class Location(models.Model):
    pass

class Shop(models.Model):
    location = models.ForeignKey(Location)

class Feed(models.Model):
     shop = models.ForeignKey()