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最近我们需要在BSC上实现代币的自动化兑换,比如自动把BNB兑换成USDT,自动把USDT兑换成CAKE等其它代币,同时也要监视价格,在价格合适的时候再兑换代币。而PancakeSwap正是BSC上最大的去中心化平台,我们已经学会了手动在PancakeSwap上进行代币兑换,那么如何使用Python对这个操作进行自动化呢?
本文从新手的角度,讲解如何在面对一个从来没接触过的新事物时,快速上手做出东西来。
我们在学习一些新知识,新编程语言,新框架的时候,往往会陷入一个误区,就是总想一来就要把东西从头到尾的啃透,在网上找了一大堆资料、书籍、视频,然后正襟危坐的从第一页开始学起,过不了多久,就会越来越枯燥,越来越疲惫,从而半途而费。
多年来我总结出了一种快速学习法,就是先借助搜索引擎看个大概,对目标事物有个基本了解,然后就直接动手开始操练,刚开始肯定是写的磕磕绊绊,但是不要紧,边写边查边改,慢慢摸索,很快就能写出个勉强能用的东西,接下来再慢慢改进,不断优化,最终改成一份能放入产品的代码,此时基本用法已经学到个七七八八了,再越到类似需求则可以融会贯通,快速做出东西。
要实现在PancakeSwap上的自动化需求,首先我们了解到,PancakeSwap的底层是一套智能合约。那么第一步我们的目标就是学会使用Python调用智能合约。
通过一番搜索我们找到了一个名为【web3.py】的库,正是做这个事情的。
初略阅读一下【web3.py】的文档,我们直接看调用合约的部分:
https://web3py.readthedocs.io/en/v5/contracts.html#contractcaller
文档中有大量的示例可以参考:
https://web3py.readthedocs.io/en/v5/examples.html
接下来马上动手操练,写一个调用合约的代码,比如调用BUSD的合约,查询我们的BUSD余额。
我们在BSC浏览器上找到BUSD的合约地址:
https://bscscan.com/address/0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56#readContract
在下方的【Contract】选项卡,我们可以看到该合约的方法,其中【Read Contract】是只读方法,用于查询一些数据,不需要签名即可调用,【Write Contract】是写入方法,需要签名授权才可以调用,我们可以直接在这边页面手动测试,比如上图中,在【balanceOf】方法中输入我们的钱包地址,点击【Query】按钮就可以查出我们的余额,由于USDT有18位小数精度,所以这个数值需要除以 10^18,就可以得到人类可读的余额约为 35.026 BUSD。其实这是一个标准的ERC20代币合约,在BSC上也称为【BEP20 Token】 标准,有着统一的ABI接口,但先不用了解那么多,我们直接上手,使用Python的【web3.py】库,调用这个合约的【balanceOf】方法:
import web3 from decimal import Decimal import json client = web3.Web3(web3.HTTPProvider("https://bsc-dataseed1.binance.org")) address_busd = "0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56" abi_busd = json.loads(r'[{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"constant":true,"inputs":[],"name":"_decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"_name","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"_symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"burn","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"subtractedValue","type":"uint256"}],"name":"decreaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"getOwner","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"addedValue","type":"uint256"}],"name":"increaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"mint","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"owner","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"renounceOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"}]') def main(): contract = client.eth.contract(address = address_busd, abi = abi_busd) balance = contract.caller.balanceOf("0xeaC7d998684F50b7A492EA68F27633a117Be201d") balance = Decimal(balance) / (10 ** 18) print(balance) if __name__ == '__main__': main()
执行结果:
果然成功调用合约拿到了余额数字
代码其中有个参数是abi_busd,即BUSD这个合约的ABI,这个ABI从哪里来呢,依然是在BSC浏览器里面查询合约地址就可以找到:
https://bscscan.com/address/0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56#code
在【Contract】的【Code】里可以找到它的ABI,是一个JSON,复制出来即可。
ABI我们可以理解为对该合约所有公开方法的描述,它声明了函数名,函数参数个数、类型,返回值,这样在调用该合约的时候才能正确的序列化参数以及获取返回值,不难理解为什么要有这么个东西,想想在Windows上的C++开发中,很多第三方闭源库都是提供一个DLL文件和一个 .h头文件和一个 .lib 导入库,.h里的函数定义就如同这些JSON ABI,描述每个函数的函数名和参数,我们才能正确调用,至于C# 的DLL为什么可以直接调用而不需要接口描述文件,那是因为它的接口描述信息已经写到了DLL中,可以直接从DLL文件读取。
那么这个合约的ABI文件,除了从BSC浏览器中手动复制,有没有办法从网络上获取呢?当然是有的,【bscscan】提供了很多API其中就包括获取合约ABI的API,文档在此:
https://docs.bscscan.com/api-endpoints/contracts
import web3 from web3.middleware import geth_poa_middleware from decimal import Decimal import requests client = web3.Web3(web3.HTTPProvider("https://bsc-dataseed1.binance.org")) # 连接公共节点需要注入此中间件 client.middleware_onion.inject(geth_poa_middleware, layer=0) # 我们的钱包地址 address_wallet = "0xeaC7d998684F50b7A492EA68F27633a117Be201d" # 私钥从环境变量获取 private_key = os.getenv("key") # BUSD合约地址 address_busd = "0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56" # pancakeswap合约地址 address_pancakeswap = "0x10ED43C718714eb63d5aA57B78B54704E256024E" # 获取合约ABI def fetch_abi(address): url = "https://api.bscscan.com/api" params = { "module": "contract", "action": "getabi", "address": address, "apikey": "6HQZV977GIY8FNT36XN1JJSE12IP2IYVTQ", } resp = requests.get(url, params = params).json() return resp["result"] # 获取账户ERC20代币余额 def erc20_balance(address_erc20: str, wallet: str) -> Decimal: abi_busd = fetch_abi(address_erc20) contract = client.eth.contract(address=address_erc20, abi=abi_busd) # 先获取该代币精度 decimals = contract.functions.decimals().call() # 获取代币余额 balance = contract.functions.balanceOf(wallet).call() balance = Decimal(balance) / (10 ** decimals) return balance def main(): balance = erc20_balance(address_busd, address_wallet) print(balance) if __name__ == '__main__': main()
于是我们写了一个Python函数用于从网上获取ABI,这样在调用不同合约的时候,就不用一一手动复制ABI了。
注意上面的 apikey 是 bscscan.com 的 apikey ,我们可以在这里注册账号免费申请:https://bscscan.com/apis
免费版的 apikey 一天可以调用10万次 bscscan API,足够使用了。
不过这种从网上获取ABI的方式,在项目实践中最好获取一次然后缓存到本地,可以存到数据库也可以存到文本文件,总之每调用一次合约函数,就要发送HTTP请求获取一次ABI,是不太明智的选择,当然我们现在是学习阶段,这样简单写一写也无妨。
接下来,我们需要调用 PancakeSwap 合约,实现代币的兑换,以BUSD兑换CAKE为例,最简单快速的方法,就是直接去 PancakeSwap 网页上手动发起一笔交易,待交易成功后,到BSC浏览器里查看链上的交易记录,看它调用了哪个合约的哪个方法,传递了什么参数,然后使用Python写代码,照葫芦画瓢即可。
首先,在 PancakeSwap 第一次交易某种代币时,需要授权,这个授权实际上是调用 BUSD 合约的【approve】方法,将我们账户的BUSD授权给 PancakeSwap 的合约进行支配,这样在接下来的兑换交易中,PancakeSwap 的合约才有权从我们账户中提取我们的BUSD代币,然后缓存CAKE代币转给我们。这个授权该如何用Python去实现呢?最简单的方法是直接提交交易,然后到BSC浏览器查询这笔交易:
https://bscscan.com/tx/0x6bdb716c91b4446dc9f66305578569241eb6b3ee058d943730a9ff3645f7994f#eventlog
在 Logs 这里我们可以看到这笔授权交易调用了
0xe9e7cea3dedca5984780bafc599bd69add087d56 合约(BUSD合约)的 Approval 方法
在【Overview】中我们可以看到传递的两个参数值是什么
再到BSC浏览器中查看BUSD的合约方法:
确实有【approve】这个方法,我们也可以直接在这里输入一样的参数进行手动测试,以验证结果。网上搜索资料,我们可以了解到这两个参数的意思,【spender】就是授权给谁,这里是授权给PancakeSwap的合约地址,【amount】是授权金额,图片里的这个值就是uint256的最大值,最终结果就等同于【无限制】。
接下来我们用Python代码实现这个授权操作:
import web3 from web3.middleware import geth_poa_middleware from decimal import Decimal import requests client = web3.Web3(web3.HTTPProvider("https://bsc-dataseed1.binance.org")) # 连接公共节点需要注入此中间件 client.middleware_onion.inject(geth_poa_middleware, layer=0) # 我们的钱包地址 address_wallet = "0xeaC7d998684F50b7A492EA68F27633a117Be201d" # 私钥从环境变量获取 private_key = os.getenv("key") # BUSD合约地址 address_busd = "0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56" # pancakeswap合约地址 address_pancakeswap = "0x10ED43C718714eb63d5aA57B78B54704E256024E" # 获取合约ABI def fetch_abi(address): url = "https://api.bscscan.com/api" params = { "module": "contract", "action": "getabi", "address": address, "apikey": "6HQZV977GIY8FNT36XN1JJSE12IP2IYVTQ", } resp = requests.get(url, params = params).json() return resp["result"] # 授权pancakeswap合约使用我们账户的BUSD代币 def approve_busd_to_pancakeswap(wallet: str): abi_busd = fetch_abi(address_busd) contract = client.eth.contract(address=address_busd, abi=abi_busd) txn = contract.functions.approve(address_pancakeswap, 2 ** 256 - 1).build_transaction({ "chainId": client.eth.chain_id, "from": wallet, "nonce": client.eth.get_transaction_count(wallet), "gasPrice": client.eth.gas_price }) signed_txn = client.eth.account.sign_transaction(txn, private_key) txn_hash = client.eth.send_raw_transaction(signed_txn.rawTransaction) txn_hash = client.toHex(txn_hash) return txn_hash def main(): txn_hash = approve_busd_to_pancakeswap(address_wallet) print(txn_hash) if __name__ == '__main__': main()
授权完成后,在进行兑换交易之前,我们需要先查询兑换价格,这样才能确定多少代币可以兑换多少另一种代币,我们以BUSD购买CAKE为例,先查询一个BUSD可以买多少个CAKE。
我们先在BSC浏览器中找到 PancakeSwap 的合约地址:
https://bscscan.com/address/0x10ed43c718714eb63d5aa57b78b54704e256024e#readContract
同理,我们在下方的【Contract】【Read Contract】中可以测试该合约的所有可读方法,其中【getAmountsOut】方法就是用于查询多少A代币可以兑换多少B代币的函数,我们可以直接在这里手动测试,其中【amountIn】参数就是输入多少A代币,【path】参数就是兑换路径,这是一个数组,这里我们填入BUSD的合约地址和CAKE的合约地址即可,表示直接从BUSD兑换成CAKE,因为这两个代币之间有一个很大的流动性池子,可以直接兑换。有的时候,要兑换的两种代币之间没有池子,则需要将A先换成B再换成C,这个时候【path】就有三个元素,分别是A/B/C代币的合约地址。
比如要把HIGH兑换成CAKE,由于HIGH和CAKE之间没有池子,所以需要先讲HIGH换成BUSD再换成CAKE,那么【path】就需要三个元素,分别是HIGH/BUSD/CAKE的合约地址。
弄清楚大致原理后,我们就可以着手写Python代码如下:
import web3 from web3.middleware import geth_poa_middleware from decimal import Decimal import requests client = web3.Web3(web3.HTTPProvider("https://bsc-dataseed1.binance.org")) # 连接公共节点需要注入此中间件 client.middleware_onion.inject(geth_poa_middleware, layer=0) # 我们的钱包地址 address_wallet = "0xeaC7d998684F50b7A492EA68F27633a117Be201d" # BUSD合约地址 address_busd = "0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56" # CAKE合约地址 address_cake = "0x0E09FaBB73Bd3Ade0a17ECC321fD13a19e81cE82" # pancakeswap合约地址 address_pancakeswap = "0x10ED43C718714eb63d5aA57B78B54704E256024E" # 获取合约ABI def fetch_abi(address): url = "https://api.bscscan.com/api" params = { "module": "contract", "action": "getabi", "address": address, "apikey": "6HQZV977GIY8FNT36XN1JJSE12IP2IYVTQ", } resp = requests.get(url, params = params).json() return resp["result"] # 查询CAKE与BUSD兑换价格 def query_cake_price() -> Decimal: abi_pancakeswap = fetch_abi(address_pancakeswap) contract = client.eth.contract(address=address_pancakeswap, abi=abi_pancakeswap) price = contract.functions.getAmountsOut(1 * 10 ** 18, [address_busd, address_cake]).call() return Decimal(price[1]) / (10 ** 18) def main(): price = query_cake_price() print(price) if __name__ == '__main__': main()
执行结果:
可以看到,执行结果为,1个BUSD可以换约0.2535个CAKE
需要注意的是,函数中的 10 ** 18,因为我们知道 BUSD 和 CAKE 的精度都是18位小数,所以我们在这里直接写死了,在实际项目中需要根据你的情况更改。
接下来最后一步就是进行兑换交易了,我们可以先手动兑换一笔,然后查看交易记录:
https://bscscan.com/tx/0x71f5d27d08803ca834b685c86b7f8a2b72039b468fc6600256a18e8ba0c7a173
我们可以看到它调用了 PancakeSwap 合约的 【swapExactTokensForTokens】方法,【Decode Input Data】后可以看到传递的参数是什么:
有同学就要问了,你怎么知道 PancakeSwap 合约的这些方法和参数是什么含义呢?包括上面的【getAmountsOut】方法,答案就在PancakeSwap的文档中,解释得很清楚了:
https://docs.pancakeswap.finance/code/smart-contracts/pancakeswap-exchange/v2/router-v2
接下来我们用 Python 代码实现兑换操作:
import web3 from web3.middleware import geth_poa_middleware from decimal import Decimal import requests from datetime import datetime, timedelta client = web3.Web3(web3.HTTPProvider("https://bsc-dataseed1.binance.org")) # 连接公共节点需要注入此中间件 client.middleware_onion.inject(geth_poa_middleware, layer=0) # 我们的钱包地址 address_wallet = "0xeaC7d998684F50b7A492EA68F27633a117Be201d" # 私钥从环境变量获取 private_key = os.getenv("key") # BUSD合约地址 address_busd = "0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56" # CAKE合约地址 address_cake = "0x0E09FaBB73Bd3Ade0a17ECC321fD13a19e81cE82" # pancakeswap合约地址 address_pancakeswap = "0x10ED43C718714eb63d5aA57B78B54704E256024E" # 获取合约ABI def fetch_abi(address): url = "https://api.bscscan.com/api" params = { "module": "contract", "action": "getabi", "address": address, "apikey": "6HQZV977GIY8FNT36XN1JJSE12IP2IYVTQ", } resp = requests.get(url, params = params).json() return resp["result"] # 将BUSD兑换为CAKE def swap_busd_to_cake(wallet: str, amount_busd: Decimal): abi_pancakeswap = fetch_abi(address_pancakeswap) contract = client.eth.contract(address=address_pancakeswap, abi=abi_pancakeswap) price_cake = contract.functions.getAmountsOut(1 * 10 ** 18, [address_busd, address_cake]).call() price_cake = Decimal(price_cake[1]) / (10 ** 18) # 滑点0.5% 交易手续费 0.25% ,则最小换得的cake数量为理论换得的cake数量 乘 99.25 % amount_cake_min = int(price_cake * amount_busd * Decimal("0.9925") * 10 ** 18) amount_busd = int(amount_busd * 10 ** 18) # deadline为交易必须在此时间前确认,否则交易失败,我们在pancakeswap网页上手动操作的时候默认是20分钟,所以照着它来 deadline = datetime.now() + timedelta(minutes = 20) txn = contract.functions.swapExactTokensForTokens(amount_busd, amount_cake_min, [address_busd, address_cake], wallet, int(deadline.timestamp())).build_transaction({ "chainId": client.eth.chain_id, "from": wallet, "nonce": client.eth.get_transaction_count(wallet), "gasPrice": client.eth.gas_price }) signed_txn = client.eth.account.sign_transaction(txn, private_key) txn_hash = client.eth.send_raw_transaction(signed_txn.rawTransaction) txn_hash = client.toHex(txn_hash) return txn_hash def main(): txn_hash = swap_busd_to_cake(address_wallet, Decimal("1.0")) print(txn_hash) if __name__ == '__main__': main()
执行以后,交易成功,perfect !
https://bscscan.com/tx/0xbb7de1e37f332bd8114ba8d58cf3a13226d76194dc8cc08f3e7dac9ba00df4a0
【python_pancakeswap】https://github.com/encoderlee/python_pancakeswap
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