code: def set_default_account_by_index(self, index: int):
          
          if index >= len(self.accounts):
              raise SDKException(ErrorCode.param_error)
          for acct in self.accounts:
              acct.is_default = False
          self.accounts[index].is_default = True
          self.default_account_address = self.accounts[index].b58_address
docs: This interface is used to set default account by given index.
  
          :param index: an int value that indicate the account object in account list.