Django form - Calling is_valid() in a template - django

Question

I'm using Django 1.5. I have a template with multiple forms: one driver has many cars (inline forms). I want to display a hint indicating which section contains errors.
The template:
{% if driver_form.is_bound and not driver_form.is_valid %}
Please correct errors in the Driver Data.
{% endif %}
{% if car_form.is_bound and not car_form.is_valid %}
Please correct errors in the Car Data.
{% endif %}
The problem is that if the first form is invalid, the second message pops up as well, even though the second form is valid. I also noticed that if I put {{ car_form.is_valid }} three times in a row, the first time it is empty, the next time (and following) it is True.
The original view:
if request.method == 'POST':
driver_form = DriverModelForm(request.POST)
car_form_set = CarInlineFormSet(request.POST) # wrong: no instance passed
if driver_form.is_valid():
driver = driver_form.save(commit=False)
car_form_set = CarInlineFormSet(request.POST, instance=driver)
if car_form_set.is_valid():
driver.save()
car_form_set.save()
else:
driver_form = DriverModelForm()
car_form_set = CarInlineFormset()
return render(request, 'template.html', {
'driver_form': driver_form,
'car_form_set': car_form_set
})
UPDATE:
It seems that for simplicity's sake I left out the details that actually caused the problem. Lesson learned.
There was a Javascript setting values on page load, while it only needed to be done on a dropdown change. It was hiding the erroneous values and causing the form to be valid next time around.
There is a dependency: driver_form is a model form, and car_form_set is an inline form set based on the instance that the driver_form is adding.
The problem was indeed in the view, as seddonym suggested: the car_form_set was not being initialized with an instance if the driver_form was invalid. So is_valid() was neither True nor False. Conclusion: using is_valid() in the template works just fine.
The fixed view:
driver = Driver()
if request.method == 'POST':
driver_form = DriverModelForm(request.POST, instance=driver)
if driver_form.is_valid():
driver = driver_form.save(commit=False)
car_form_set = CarInlineFormSet(request.POST, instance=driver)
if car_form_set.is_valid():
driver.save()
car_form_set.save()
else:
driver_form = DriverModelForm(instance=driver)
car_form_set = CarInlineFormset(instance=driver)
return render(request, 'template.html', {
'driver_form': driver_form,
'car_form_set': car_form_set
})

Answer 1

You don't need to call form.is_valid, that will already have been called by the view. Instead, check for errors:
{% if first_form.errors %}
Please correct errors in the First Form.
{% endif %}
{% if second_form.errors %}
Please correct errors in the Second Form.
{% endif %}