Handle a valid upload form.

def form_upload_valid(self, form):
        """Handle a valid upload form."""
        self.current_step = self.STEP_LINES

        lines = form.cleaned_data['file']
        initial_lines = [dict(zip(self.get_columns(), line)) for line in lines]
        inner_form = self.get_form(self.get_form_class(),
            data=None,
            files=None,
            initial=initial_lines,
        )
        return self.render_to_response(self.get_context_data(form=inner_form))