# forms.py
class ProfileForm(forms.ModelForm):

    city = forms.ModelChoiceField(queryset=None)

    def __init__(self, *args, **kwargs):
        if 'region' in kwargs:
            # добавление городов только из указанного региона
            region = kwargs.pop('region')
            super(ProfileForm, self).__init__(*args, **kwargs)
            self.fields['city'].queryset = region.city_set.all()
        elif 'data' in kwargs:
            # при создании bound form нужно взять регион из данных
            # если оставить queryset пустым, то форма не будет валидна
            # к тому же, форма не должна терять данные юзера между сабмитами
            super(ProfileForm, self).__init__(*args, **kwargs)
            region_id = self['region'].value()
            region = Region.objects.get(pk=region_id)
            self.fields['city'].queryset = region.city_set.all()

    class Meta:
        model = Profile
        fields = ['country', 'region']


# views.py
def signup(request):
    if request.method == 'POST':
        pform = ProfileForm(data=request.POST)
        if pform.is_valid():
            return HttpResponse('%s' % pform)
    else:
        # определение гео пришедшего юзера
        ip = request.META.get('REMOTE_ADDR', '') or request.META.get(
               'HTTP_X_FORWARDED_FOR', '')
        info = get_ip_info(ip)
        region = Region.objects.filter(name__contains=info['region'])[0]
        city = City.objects.filter(name__contains=info['city'])[0]

        pform = ProfileForm(region=region,
                            initial={'region': region.id, 'city': city.id,
                                    'country': 1
                                    })
    return render(request, 'authenticate/signup.html', {
        'pform': pform,
        'message': message,
    })

# тут все стандартно
# models.py
class Country(models.Model):
    id = models.IntegerField(primary_key=True)
    name = models.CharField(max_length=100)
    rank = models.IntegerField(default=0)

    def __str__(self):
        return '{}'.format(self.name)


class Region(models.Model):
    id = models.IntegerField(primary_key=True)
    name = models.CharField(max_length=100)
    country = models.ForeignKey(Country, on_delete=models.CASCADE, default=0)
    rank = models.IntegerField(default=0)

    def __str__(self):
        return '{}'.format(self.name)

class City(models.Model):
    id = models.IntegerField(primary_key=True)
    region = models.ForeignKey(Region, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)
    center = models.BooleanField(default=False)
    rank = models.IntegerField(default=0)

    def __str__(self):
        return '{}'.format(self.name)

class Profile(models.Model):
    id = models.IntegerField(primary_key=True)
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                            on_delete=models.CASCADE)
    country = models.ForeignKey(Country, on_delete=models.CASCADE)
    region = models.ForeignKey(Region, on_delete=models.CASCADE)
    city = models.ForeignKey(City, on_delete=models.CASCADE)
    bday = models.DateField()