以太坊：通过Web3实现智能合约交互

1. 环境准备

1.1 安装相关依赖包

安装pip3

sudo apt install python3-pip -y

使用pip3安装web3 python包

pip3 install web3

安装ipython3

sudo apt install ipython3 -y

1.2 安装ganache

下载

输入以下命令，运行ganache（./后的内容视具体版本而定）

./ganache-2.5.4-linux-x86_64.AppImage &

1.3 测试

进入Python交互环境

ipython3

输入以下代码测试连接情况

from web3 import Web3
w3 = Web3(Web3.HTTPProvider("http://localhost:7545"))
w3.isConnected()

2. 新建一个student合约

2.1 配置合约信息

在contracts文件夹中新建Student.sol并输入以下内容:

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.16 <0.9.0;

contract Student{

    string name;

    constructor() {
        // name = _name;
        name = "Tom";
    }

    function getName() public view returns (string memory) {
        return name;
    }

}

2.2 编写web3脚本

2.2.1新建一个Student.py文件

导入库

from web3 import Web3
import os
import sys
import getopt
import uuid

声明一些全局变量

url = "http://localhost:7545"   				# 以太坊测试链 rpc 连接端口
contract_address_file = contract_student.txt  # 合约地址保存文件
abi_file = "Student/Student.abi"  				# abi 文件
bytecode_file = "Student/Student.bin"  			# 字节码文件
account_id = 0									# 默认账户

连接测试链

# 连接测试链
w3 = Web3(Web3.HTTPProvider(url))   
eth = w3.eth
print("eth connect:", w3.isConnected())

设置默认账户

def set_default_account():
    """
        设置调用合约、发送交易的账户
    """
    global account_id
    eth.defaultAccount = eth.accounts[account_id]

获取abi和bytecode

def get_abi_from_file(file):
    """
       从文件中获取abi
    """
    with open(file, r) as f:
        return f.read() 

def get_bytecode_from_file(file):
    """
        从文件中获取字节码
    """
    with open(file, r) as f:
        return "0x" + f.read()

部署合约、获取合约地址

def deploy_contract(abi, bytecode):
    """
        部署合约
    """
    contract = eth.contract(abi=abi, bytecode=bytecode)     # 创建合约
    tx_hash = contract.constructor().transact()             # 部署合约（发送构造函数的交易，需相对应合约中的参数）
    tx_receipt = eth.waitForTransactionReceipt(tx_hash)     # 等待交易回执
    print("contract address:", tx_receipt.contractAddress)  # 合约地址
    # 保存合约
    global contract_address_file
    with open(contract_address_file, "w") as f:
        f.write(tx_receipt.contractAddress)
    # 通过地址获取已部署合约
    deployed_contract = eth.contract(address=tx_receipt.contractAddress, abi=abi)
    return deployed_contract

def get_deployed_contract(abi, bytecode):
    """
        获取部署合约，如果本地已保存合约地址，则调用该地址的合约，否则重新创建一个新的合约
    """
    try:
        # 尝试获取已有合约
        with open(contract_address_file, "r") as f:
            contract_address = f.read()
        print("contract address:", contract_address)
        deployed_contract = eth.contract(address=contract_address, abi=abi)
        return deployed_contract
    except IOError:
        # 获取已有合约失败则重新部署新合约
        return deploy_contract(abi, bytecode)

main方法

if __name__ == __main__:
    set_default_account()
    abi = get_abi_from_file(abi_file)
    bytecode = get_bytecode_from_file(bytecode_file)
    deployed_contract = get_deployed_contract(abi, bytecode)
    print(deployed_contract.functions.getName().call())

2.2.2 编译合约与运行

编译

solc --abi --bin --overwrite -o Student Student.sol

运行

python3 Student.py