Django override of ModelForm init methods

# views.py
@login_required
def create_payment(request):
    user = request.user
    if not user.vehicle_set.all():
        return redirect("vehicle_auth_send")
    else:
        if request.method == 'POST':
            form = PaymentForm(user=user, data=request.POST)
            if form.is_valid():
                form.save()
                return redirect('home')
        else:
            form = PaymentForm(user=user)

        return render(request, 'forms.html', {'form': form})

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

    class Meta:
        model = Payment

    def __init__(self, user=None, *args, **kwargs):
        super(PaymentForm, self).__init__(*args, **kwargs)

        # pass in user and override queryset for ModelChoiceField
        self._user = user
        vehicles = self._user.vehicle_set.all().prefetch_related('ticket_set')
        ticket_list= []
        for i in vehicles:
            for j in i.ticket_set.all():
                if j.sum_outstanding():
                    ticket_list.append(j.pk)
        self.ticket_queryset = Ticket.objects.filter(pk__in=ticket_list)
        self.fields['ticket'].queryset = self.ticket_queryset

    def save(self, commit=True):
        instance = super(PaymentForm, self).save(commit=False)
        instance.user = self._user
        if commit:
            instance.save()
        return instance