code: def _render_headers(self, sheet):
          
          headers = getattr(self, 'headers', ())
          labels = [header['label'] for header in headers]
          extra_headers = getattr(self, "extra_headers", ())
          labels.extend([header['label'] for header in extra_headers])
          sheet.writerow(labels)
docs: Write the headers row
  
          :param obj sheet: an odswriter Sheet object