# This code is Public Domain where the Public Domain exists,
# and covered by an MIT-license everywhere else (that is: 
# do as you wish with it, but you don't get to blame me 
# for anything)

class Demo(models.Model):
    a = models.IntegerField()
    b = models.IntegerField()
    c = models.IntegerField()

class DemoForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super(DemoForm, self).__init__(*args, **kwargs)
        # order now: a b c
        value = self.fields.pop('c')
        new_pos = self.fields.keyOrder.index('b')
        self.fields.insert(pos, 'c', value)
        # order now: a c b

    class Meta:
        model = 'Demo'