code: def balance(self):
          
          if self._balance is None:
              self._balance = BalanceList(self._version, account_sid=self._solution['sid'], )
          return self._balance
docs: Access the balance
  
          :returns: twilio.rest.api.v2010.account.balance.BalanceList
          :rtype: twilio.rest.api.v2010.account.balance.BalanceList