code: def new_sheet(self, name=None, cols=None):
          
          sheet = Sheet(self.dom, name, cols)
          self.sheets.append(sheet)
          return sheet
docs: Create a new sheet in the spreadsheet and return it so content can be added.
          :param name: Optional name for the sheet.
          :param cols: Specify the number of columns, needed for compatibility in some cases
          :return: Sheet object