tokenToEthInput通过token.balanceOf获得代币兑换合约当前的代币ERC20代币存储量，然后用getInputPrice获得可兑换到的ETH的数量，接着用as_wei_value将单位转换成wei后用send函数将eth发送给接收者，最后再调用transferForm从buyer手中收取应当支付的代币。
#dev Pricing function for converting between ETH and Tokens.
#param input_amount Amount of ETH or Tokens being sold.
案例及设计I35详细7O98开发O7I8
#param input_reserve Amount of ETH or Tokens(input type)in exchange reserves.
#param output_reserve Amount of ETH or Tokens(output type)in exchange reserves.
#return Amount of ETH or Tokens bought.关于区块链项目技术开发唯:MrsFu123，代币发行、dapp智能合约开发、链游开发、多链钱包开发
交易所开发、量化合约开发、互助游戏开发、Nft数字藏品开发、众筹互助开发、元宇宙开发、swap开发、
链上合约开发、ido开发、商城开发等，开发过各种各样的系统模式，更有多种模式、制度、案例、后台等，成熟技术团队，欢迎实体参考。
private
constant
def getInputPrice(input_amount:uint256,input_reserve:uint256,output_reserve:uint256)->uint256:
assert input_reserve>0 and output_reserve>0#需要两币的储备都大于0
input_amount_with_fee:uint256=input_amount*997#抽取千分之3手续费
numerator:uint256=input_amount_with_fee*output_reserve
denominator:uint256=(input_reserve*1000)+input_amount_with_fee
return numerator/denominator
private
def tokenToEthOutput(eth_bought:uint256(wei),max_tokens:uint256,deadline:timestamp,buyer:address,recipient:address)->uint256:
assert deadline>=block.timestamp and eth_bought>0
token_reserve:uint256=self.token.balanceOf(self)#获取代币储备量
#通过getOutputPrice计算所需要花费的代币数量
tokens_sold:uint256=self.getOutputPrice(as_unitless_number(eth_bought),token_reserve,as_unitless_number(self.balance))
#tokens sold is always>0
assert max_tokens>=tokens_sold
send(recipient,eth_bought)#向接收者发送所兑换得到的ETH
assert self.token.transferFrom(buyer,self,tokens_sold)#从购买者收取代币
log.EthPurchase(buyer,tokens_sold,eth_bought)
return tokens_sold
