Write the headers row

def _render_headers(self):
        """
        Write the headers row
        """
        headers = getattr(self, 'headers', ())
        for index, col in enumerate(headers):
            # We write the headers
            cell = self.worksheet.cell(row=1, column=index + 1)
            cell.value = col['label']

        index += 1

        extra_headers = getattr(self, 'extra_headers', ())
        for add_index, col in enumerate(extra_headers):
            cell = self.worksheet.cell(row=1, column=add_index + index + 1)
            cell.value = col['label']