Class MyClass(models.Model):
    my_field = models.CharField(max_length=100,...)

Class MyClass(models.Model):
    FOO = 0
    BAR = 1
    FOO_BAR_CHOICES = (
        (FOO, 'foo')
        (BAR, 'bar')
    )
    my_field = models.ChoiceField(choices=FOO_BAR_CHOICES,...)