[区块链]Python Web3 智能合约(Smart Contract)交互（例子与POAP合约交互）

环境Python3.8

封装包依赖

pip install --upgrade pip
pip install web3

智能合约(Smart Contract)

智能合约（Solidity代码）是Web3建设的基础，是搭建去中心化生态的奠基。智能合约允许在没有第三方的情况下进行可信交易，这些交易可追踪且不可逆转。

contract ERC721 {
    function balanceOf(address _owner) external view returns (uint256);
    function ownerOf(uint256 _tokenId) external view returns (address);
    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;
    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;
    function transferFrom(address _from, address _to, uint256 _tokenId) external payable;
    function approve(address _approved, uint256 _tokenId) external payable;
    function setApprovalForAll(address _operator, bool _approved) external;
    function getApproved(uint256 _tokenId) external view returns (address);
    function isApprovedForAll(address _owner, address _operator) external view returns (bool);
    function supportsInterface(bytes4 interfaceID) external view returns (bool);
    event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
    event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);
}

Python Web3 与智能合约的交互

开发合约，或者开源合约，都会有一份该合约的ABI JSON文件

ABI文件包括了智能合约的输入与输出格式（其中name对应合约function的名字）

假如我们现在要对POAP合约交互，则需要一下
1. POAP合约地址：0x22C1f6050E56d2876009903609a2cC3fEf83B415

2. POAP合约主网的HTTPProvider:?https://dai.poa.network （HTTPProvider是链上交互的接口）

3. POAP合约的API：abi.json文件

from web3 import Web3
import web3

CONTRACT = '0x22C1f6050E56d2876009903609a2cC3fEf83B415' # 合约地址
HTTPProvider = "https://dai.poa.network"                # 主网HttpProvider

# --- 打开abi json文件
with open('contracts/contract_abi.json', 'r') as contract_abi:
		abi = json.load(contract_abi)

# --- 提供HTTPProvider，链上互动的接口
w3 = Web3(Web3.HTTPProvider(HTTPProvider))

# --- 检查HTTPProvider
print(w3.isConnected())

?HttpProvider可使用情况下输出为【True】

# --- 继续

# --- 连接合约
contract = w3.eth.contract(address=CONTRACT, abi=abi)

# --- 使用合约功能
ACC = '0xAdA556CcC02cc968579FF5294D52DC0eBf5eE328' # 个人钱包地址我随便找的
balance = contract.functions.balanceOf(acc).call() # 查询个人钱包地址的余额
print(balance)

输出为【2】