web3.contract.functions.getAmount() 中的差异

Question

我正在使用 Web3.py，但遇到了一些奇怪的事情。

对于以下代码（使用 Pancake Router V2）：

from web3 import Web3
from web3.middleware import geth_poa_middleware

web3 = Web3(Web3.HTTPProvider('https://bsc-dataseed1.binance.org:443'))
web3.middleware_onion.inject(geth_poa_middleware, layer=0)

ABI = {"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"}],"name":"getAmountsOut","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"view","type":"function"}

CAKE_ROUTER_V2 = web3.toChecksumAddress('0x10ed43c718714eb63d5aa57b78b54704e256024e')
router_contract = web3.eth.contract(address=CAKE_ROUTER_V2, abi=ABI),

WBNB = web3.toChecksumAddress('0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c')
CAKE = web3.toChecksumAddress('0x0e09fabb73bd3ade0a17ecc321fd13a19e81ce82')
KONGSHIBA = web3.toChecksumAddress('0x126f5f2a88451d24544f79d11f869116351d46e1')

print(router_contract.functions.getAmountsOut(1, [WBNB, CAKE]).call())
print(router_contract.functions.getAmountsOut(1, [WBNB, KONGSHIBA]).call())

我得到以下信息：

[1, 19]
[1, 160]

WBNB 和 CAKE 有 18 位小数，KONGSHIBA 有 17 位
。CAKE 目前的价值约为 27.7 美元，WBNB 为 545.41291093 美元
，KONGSHIBA 为 0.00000000000000000332 美元。
所以我应该回来：

[1, 19]
[1, 16000000000000000000]

请指教。

Answer 1

计算代币价格的正确方法是询问流动性池（该代币与本地 PEG 或某些美元代币的对）插入的 PEG 数量与代币数量的比率（有关流动性的更多详细信息）池表示，请参阅https://uniswap.org/docs/v2/core-concepts/pools/）。

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所以对于 python 使用：

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from web3 import Web3\nfrom web3.middleware import geth_poa_middleware # Needed for Binance\n\nfrom json import loads\nfrom decimal import Decimal\n\n\nETHER = 10 ** 18\n\nWBNB = \'0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c\'\nCAKE_ROUTER_V2 = web3.toChecksumAddress(\'0x10ed43c718714eb63d5aa57b78b54704e256024e\')\n\nweb3 = Web3(Web3.HTTPProvider(\'https://bsc-dataseed1.binance.org:443\'))\nweb3.middleware_onion.inject(geth_poa_middleware, layer=0) # Again, this is needed for Binance, not Ethirium\n\nABI = loads(\'[{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"token0","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"inputs":[],"name":"factory","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"","type":"address"},{"internalType":"address","name":"","type":"address"}],"name":"getPair","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"getReserves","outputs":[{"internalType":"uint112","name":"_reserve0","type":"uint112"},{"internalType":"uint112","name":"_reserve1","type":"uint112"},{"internalType":"uint32","name":"_blockTimestampLast","type":"uint32"}],"payable":false,"stateMutability":"view","type":"function"}]\')\n\ndef get_price(token, decimals, pair_contract, is_reversed, is_price_in_peg):\n    peg_reserve = 0\n    token_reserve = 0\n    (reserve0, reserve1, blockTimestampLast) = pair_contract.functions.getReserves().call()\n    \n    if is_reversed:\n        peg_reserve = reserve0\n        token_reserve = reserve1\n    else:\n        peg_reserve = reserve1\n        token_reserve = reserve0\n    \n    if token_reserve and peg_reserve:\n        if is_price_in_peg:\n            # CALCULATE PRICE BY TOKEN PER PEG\n            price = (Decimal(token_reserve) / 10 ** decimals) / (Decimal(peg_reserve) / ETHER)\n        else:\n            # CALCULATE PRICE BY PEG PER TOKEN\n            price = (Decimal(peg_reserve) / ETHER) / (Decimal(token_reserve) / 10 ** decimals)\n        \n        return price\n        \n    return Decimal(\'0\')\n\n\nif __name__ == \'__main__\':\n    CAKE_FACTORY_V2 = web3.eth.contract(address=CAKE_ROUTER_V2, abi=ABI).functions.factory().call()\n\n    token = web3.toChecksumAddress(\'0x126f5f2a88451d24544f79d11f869116351d46e1\')\n    pair = web3.eth.contract(address=CAKE_FACTORY_V2, abi=ABI).functions.getPair(token, WBNB).call()\n    pair_contract = web3.eth.contract(address=pair, abi=ABI)\n    is_reversed = pair_contract.functions.token0().call() == WBNB\n    decimals = web3.eth.contract(address=token, abi=ABI).functions.decimals().call()\n    is_price_in_peg = True\n\n    print(get_price(token, decimals, pair_contract, is_reversed, is_price_in_peg), \'BNB\')\n\n\n

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对于 JS 使用：

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var ETHER = Math.pow(10, 18);\n\nvar WBNB = \'0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c\';\nvar CAKE_ROUTER_V2 = Web3.utils.toChecksumAddress(\'0x10ed43c718714eb63d5aa57b78b54704e256024e\');\n\nvar web3 = new Web3(\'https://bsc-dataseed1.binance.org:443\');\n\nvar ABI = [{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"token0","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"inputs":[],"name":"factory","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"","type":"address"},{"internalType":"address","name":"","type":"address"}],"name":"getPair","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"getReserves","outputs":[{"internalType":"uint112","name":"_reserve0","type":"uint112"},{"internalType":"uint112","name":"_reserve1","type":"uint112"},{"internalType":"uint32","name":"_blockTimestampLast","type":"uint32"}],"payable":false,"stateMutability":"view","type":"function"}];\n\n\nvar get_price = async function(token, decimals, pair_contract, is_reverse, is_price_in_peg) {\n    var price,\n        peg_reserve = 0,\n        token_reserve = 0,\n        res = await pair_contract.methods.getReserves().call(),\n        reserve0 = res[0],\n        reserve1 = res[1];\n        \n    if (is_reverse) {\n        peg_reserve = reserve0;\n        token_reserve = reserve1;\n    } else {\n        peg_reserve = reserve1;\n        token_reserve = reserve0;\n    }\n    \n    if (token_reserve && peg_reserve) {\n        if (is_price_in_peg) {\n            // CALCULATE PRICE BY TOKEN PER PEG\n            price = (Number(token_reserve) / Number(Math.pow(10, decimals))) / (Number(peg_reserve) / Number(ETHER));\n        } else {\n            // CALCULATE PRICE BY PEG PER TOKEN\n            price = (Number(peg_reserve) / Number(ETHER)) / (Number(token_reserve) / Number(Math.pow(10, decimals)));\n        }\n            \n        return price;\n    }\n    \n    return Number(0);\n};\n\n\nvar token = Web3.utils.toChecksumAddress(\'0x126f5f2a88451d24544f79d11f869116351d46e1\');\nvar pair = await (await (new web3.eth.Contract(ABI, CAKE_FACTORY_V2))).methods.getPair(token, WBNB).call();\nvar pair_contract = await new web3.eth.Contract(ABI, pair);\nvar is_reversed = (await pair_contract.methods.token0().call()) == WBNB;\nvar decimals = await (await new web3.eth.Contract(ABI, token)).methods.decimals().call();\nvar is_price_in_peg = true;\n\nconsole.log(await get_price(token, decimals, pair_contract, is_reversed, is_price_in_peg), \'BNB\')\n

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注 1：这仅适用于对 WBNB 具有流动性的代币。如果流动性针对其他某种代币，您必须递归地了解该链中的所有价格并将它们相互关联，直到达到 WBNB（或其他网络中的任何其他 PEG）。

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注2.根据https://arxiv.org/pdf/2009.14021.pdf：

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预期执行价格 (E[P])：当流动性\n接受者在 X/Y 上发出交易时，\n接受者希望以\n预期执行价格\nE[P]执行交易（基于 AMM 算法和 X/ Y 状态），\n考虑到预期的滑点。

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执行价格 (P)：在流动性接受者发出交易与执行交易（例如在区块中开采）之间的时间差期间，AMM 市场 X/Y 的状态可能会发生变化。这种状态变化可能会发生变化。引起意外滑点\n导致执行价格 P != E[P]。

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意外价格滑点 (P \xe2\x88\x92 E[P])：是 P 和 E[P] 之间的差值。

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意外滑点率 ((P \xe2\x88\x92 E[P]) / E[P])：是\n超过预期价格的意外滑点。

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因此，在我们的情况下，是E[P]我们的结果， 是金额（例如 1Kwei）除以我们提供的金额（本例中为 1K）的结果，因此我们甚至可以通过最终减去来计算滑点get_price()PgetAmounsOut()P \xe2\x88\x92 E[P]

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