docs: def export_xlsx(self, key):
          """
          Download xlsx version of spreadsheet.
          """
          spreadsheet_file = self.client.files().get(fileId=key).execute()
          links = spreadsheet_file.get('exportLinks')
          downloadurl = links.get('application/vnd.openxmlformats-officedocument.spreadsheetml.sheet')
          resp, content = self.client._http.request(downloadurl)
          return content