How to write good form validation in Django?

I've seen Django's samples and I can see they have decent error handling. However I want to see if there is yet a better approach, a general pattern to handle form validation errors in Django. This is the sample I found here:

def contact(request):
    if request.method == 'POST': # If the form has been submitted...
        form = ContactForm(request.POST) # A form bound to the POST data
        if form.is_valid(): # All validation rules pass
            # Process the data in form.cleaned_data
            # ...
            return HttpResponseRedirect('/thanks/') # Redirect after POST
    else:
        form = ContactForm() # An unbound form

    return render_to_response('conta开发者_JAVA百科ct.html', {
        'form': form,
    })

In particular, I was wondering:

1. How can the view in "/thanks/" be sure that the form was validated? Are there any common ways to pass the successful validation of the form to the next view? Or do I need to do something manually such as setting a flag in request's session?

2. How can one write this code in a way that when form is NOT valid and the page is shown with errors upon submission, if user refreshes the browser it wouldn't ask the user if they want to POST data again?

EDIT: With regards to #1 I am referring to cases like user manually entering the '/thanks/' url or going back and forth through history pages and accidentally openning it without any form being validated. (Do we still show the "thanks" page? or we need to somehow re-validate why we are in thanks view).

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1. The view can be sure that the form is validated because it will only be called if the form is valid...

2. If the page is generated through a post request the browser will always ask you that when hitting refresh... I guess the only way to avoid this would be redirecting to another page!

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How can the view in "/thanks/" be sure that the form was validated?

form.is_valid() should thoroughly check any field or - if necessary - any combination, cornercase, etc. That's basically it. The views knows, the form was valid if it renders. There is no need to include redundant information in the session.

How can one write this code in a way that when form is NOT valid and the page is shown with errors upon submission, if user refreshes the browser it wouldn't ask the user if they want to POST data again?

I am not sure what the point would be. The form contains errors and the user may correct them or leave. To render a page that would not ask for form resubmission, one could use a redirect, just as in the valid case. The error markup would have to be done manually in that case.