【BSC】使用Python玩转PancakeSwap（入门篇）

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需求

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

快速学习法

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。

调用合约

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

在这里插入图片描述

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
在这里插入图片描述
果然成功调用合约拿到了余额数字

合约ABI

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

在这里插入图片描述
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。

授权

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。
在这里插入图片描述
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
在这里插入图片描述
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
在这里插入图片描述
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
在这里插入图片描述
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()

查询价格

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
在这里插入图片描述
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。
在这里插入图片描述
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
在这里插入图片描述
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。

兑换交易

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
在这里插入图片描述
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
在这里插入图片描述
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
在这里插入图片描述

完整示例代码

【python_pancakeswap】https://github.com/encoderlee/python_pancakeswap

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