title: How should I deal with a MultiValueDictKeyError?
body: <p>I am working on a checkout form for my app but when i submit, Django returns a <code>MultiValueDictKeyError</code> exception.</p>
  
  <pre><code>Traceback:
  File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
    111.                         response = callback(request, *callback_args, **callback_kwargs)
  File "/home/mats-invasion/projects/f4l/f4l/live/views.py" in show_checkout
    33.           if postdata['submit'] == 'place_order':
  File "/home/mats-invasion/projects/f4l/env/local/lib/python2.7/site-packages/django/utils/datastructures.py" in __getitem__
    258.             raise MultiValueDictKeyError("Key %r not found in %r" % (key, self))
  
  Exception Type: MultiValueDictKeyError at /orders/checkout/
  Exception Value: "Key 'submit' not found in &lt;QueryDict: {u'delivery_address': [u'klab Telecom House,6th floor'], u'billing_address': [u'klab 6th telecom house'], u'billing_city': [u'kigza'], u'phone': [u'+2500855598432'], u'billing_name': [u'mar'], u'credit_card_type': [u'VISA'], u'credit_card_expire_month': [u'01'], u'credit_card_number': [u'4007000000027'], u'delivery_name': [u'mar'], u'credit_card_cvv': [u'567'], u'credit_card_expire_year': [u'2016'], u'csrfmiddlewaretoken': [u'UGu4G75x2CxPFfnUdGSnVZzueedNxtu6'], u'delivery_city': [u'kigali'], u'email': [u'marxmass@gmail.com']}&gt;"
  </code></pre>
  
  <p>Here is the form view:</p>
  
  <pre><code>def show_checkout(request):
      if order.is_empty(request):
          cart_url = urlresolvers.reverse('order_index')
          return HttpResponseRedirect(cart_url)
      if  request.method == 'POST':
          postdata = request.POST.copy()
          form = CheckoutForm(postdata)
          if form.is_valid():
              response = checkout.process(request)
              order_number = response.get('order_number',0)
              error_message = response.get('message','')
              if order_number:            
                  request.session['order_number'] = order_number
              if postdata['submit'] == 'place_order':
                  reciept_url = urlresolvers.reverse('checkout_reciept')
                  return HttpResponseRedirect(reciept_url)
      else:
          form = CheckoutForm()
      context = {
          'form':form,
      }
      return render_to_response('checkout/checkout.html',context,context_instance=RequestContext(request))
  </code></pre>
  
  <p>Here is what a, doing in my template,</p>
  
  <pre><code>&lt;input type="submit" value="Place order" class="submit" /&gt;
  </code></pre>
  
  <p>Any assistance is appreciated..</p>