old_contents: from django.core.urlresolvers import reverse
  from django.utils.translation import ugettext_lazy as _
  from oscar.apps.checkout import session, exceptions
  from oscar_vat_moss import vat
  
  
  class CheckoutSessionMixin(session.CheckoutSessionMixin):
  
      def build_submission(self, **kwargs):
          submission = super(CheckoutSessionMixin, self).build_submission(
              **kwargs)
  
          assess_tax = (submission['shipping_method']
                        and submission['shipping_address']
                        and submission['shipping_address'].phone_number)
          if assess_tax:
              try:
                  vat.apply_to(submission)
                  # Recalculate order total to ensure we have a
                  # tax-inclusive total
                  submission['order_total'] = self.get_order_totals(
                      submission['basket'], submission['shipping_charge'])
              except vat.VATAssessmentException:
                  pass
          return submission
  
      def check_a_valid_shipping_address_is_captured(self):
          super(CheckoutSessionMixin, self)
          shipping_address = self.get_shipping_address(
              basket=self.request.basket)
          try:
              vat.lookup_vat_for_shipping_address(shipping_address)
          except vat.VATAssessmentException as e:
              message = _("%s. Please try again." % str(e))
              raise exceptions.FailedPreCondition(
                  url=reverse('checkout:shipping-address'),
                  message=message
              )
  
      def get_context_data(self, **kwargs):
          ctx = super(CheckoutSessionMixin, self).get_context_data(**kwargs)
  
          # Oscar's checkout templates look for this variable which specifies to
          # break out the tax totals into a separate subtotal.
          ctx['show_tax_separately'] = True
  
          return ctx
  
new_contents: from django.core.urlresolvers import reverse
  from django.utils.translation import ugettext_lazy as _
  from oscar.apps.checkout import session, exceptions
  from oscar_vat_moss import vat
  
  
  class CheckoutSessionMixin(session.CheckoutSessionMixin):
  
      def build_submission(self, **kwargs):
          submission = super(CheckoutSessionMixin, self).build_submission(
              **kwargs)
  
          assess_tax = (submission['shipping_method'] and
                        submission['shipping_address'] and
                        submission['shipping_address'].phone_number)
          if assess_tax:
              try:
                  vat.apply_to(submission)
                  # Recalculate order total to ensure we have a
                  # tax-inclusive total
                  submission['order_total'] = self.get_order_totals(
                      submission['basket'], submission['shipping_charge'])
              except vat.VATAssessmentException:
                  pass
          return submission
  
      def check_a_valid_shipping_address_is_captured(self):
          super(CheckoutSessionMixin, self)
          shipping_address = self.get_shipping_address(
              basket=self.request.basket)
          try:
              vat.lookup_vat_for_shipping_address(shipping_address)
          except vat.VATAssessmentException as e:
              message = _("%s. Please try again." % str(e))
              raise exceptions.FailedPreCondition(
                  url=reverse('checkout:shipping-address'),
                  message=message
              )
  
      def get_context_data(self, **kwargs):
          ctx = super(CheckoutSessionMixin, self).get_context_data(**kwargs)
  
          # Oscar's checkout templates look for this variable which specifies to
          # break out the tax totals into a separate subtotal.
          ctx['show_tax_separately'] = True
  
          return ctx
  
subject: Fix PEP8 warning (W503)