Don't show country field if only one is available

This affects the shipping address form in checkout.

oscar/apps/checkout/forms.py

 from oscar.core.compat import get_user_model
 
 User = get_user_model()
+Country = get_model('address', 'Country')
 
 
 class ShippingAddressForm(AbstractAddressForm):
 
     def __init__(self, *args, **kwargs):
         super(ShippingAddressForm, self).__init__(*args, **kwargs)
-        self.set_country_queryset()
-        self.fields['country'].empty_label = None
+        countries = Country._default_manager.filter(
+            is_shipping_country=True)
 
-    def set_country_queryset(self):
-        self.fields['country'].queryset = get_model(
-            'address', 'country')._default_manager.filter(
-                is_shipping_country=True)
+        # No need to show country dropdown if there is only one option
+        if len(countries) == 1:
+            del self.fields['country']
+            self.instance.country = countries[0]
+        else:
+            self.fields['country'].queryset = countries
+            self.fields['country'].empty_label = None
 
     class Meta:
         model = get_model('order', 'shippingaddress')

oscar/apps/checkout/views.py

         return UserAddress._default_manager.filter(user=self.request.user).order_by('-is_default_for_shipping')
 
     def post(self, request, *args, **kwargs):
-        # Check if a shipping address was selected directly (eg no form was filled in)
+        # Check if a shipping address was selected directly (eg no form was
+        # filled in)
         if self.request.user.is_authenticated() and 'address_id' in self.request.POST:
-            address = UserAddress._default_manager.get(pk=self.request.POST['address_id'],
-                                                       user=self.request.user)
+            address = UserAddress._default_manager.get(
+                pk=self.request.POST['address_id'], user=self.request.user)
             action = self.request.POST.get('action', None)
             if action == 'ship_to':
                 # User has selected a previous address to ship to
             else:
                 return HttpResponseBadRequest()
         else:
-            return super(ShippingAddressView, self).post(request, *args, **kwargs)
+            return super(ShippingAddressView, self).post(
+                request, *args, **kwargs)
 
     def form_valid(self, form):
         # Store the address details in the session and redirect to next step
-        self.checkout_session.ship_to_new_address(form.clean())
+        address_fields = dict(
+            (k, v) for (k, v) in form.instance.__dict__.items()
+            if not k.startswith('_'))
+        self.checkout_session.ship_to_new_address(address_fields)
         return super(ShippingAddressView, self).form_valid(form)
 
     def get_success_url(self):