从 Python 调用智能合约

以太坊带来了智能合约的进步，其是可公开验证的代码。如果我们改变合约状态，我们将花费一些gas。现在，让我们创建一个Python程序，它可以在以太坊上调用智能合约。因为我们不想实验中支付费用，所以我们将运行Ganache，这是一个本地以太坊实例。

首先，我们去Remix.ethereum.org并添加我们的代码：

我们添加的代码中包括add()， sub()， mul()， sqr()和sqrt()函数：

pragma solidity ^0.8.0;

contract mymath {

function sqrt(uint x) public view returns (uint y) {
    uint z = (x + 1) / 2;
    y = x;
    while (z < y) {
        y = z;
        z = (x / z + z) / 2;
    }
}
function sqr(uint a) public view returns (uint) {
    uint c = a * a;
    return c;
  }
function mul(uint a, uint b) public view returns (uint) {
    uint c = a * b;
    return c;
  }
function sub(uint a, uint b) public view returns (uint) {
    return a - b;
  }
function add(uint a, uint b) public view returns (uint) {
    uint c = a + b;
    return c;
}}

现在编译我们的智能合约，并生成ABI(应用程序二进制接口)。通过ABI，我们可以创建智能合约中所有数据元素和函数。这通常用JSON格式定义。在我们的例子中，ABI是(可以从Remix中的ABI复制按钮中复制):

  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "a",
        "type": "uint256"
      },
      {
        "internalType": "uint256",
        "name": "b",
        "type": "uint256"
      }
    ],
    "name": "add",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "a",
        "type": "uint256"
      },
      {
        "internalType": "uint256",
        "name": "b",
        "type": "uint256"
      }
    ],
    "name": "mul",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "a",
        "type": "uint256"
      }
    ],
    "name": "sqr",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "x",
        "type": "uint256"
      }
    ],
    "name": "sqrt",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "y",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "a",
        "type": "uint256"
      },
      {
        "internalType": "uint256",
        "name": "b",
        "type": "uint256"
      }
    ],
    "name": "sub",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  }

接下来，我们运行 Ganache：

然后可以选择Ganache作为我们的环境：

下一步部署智能合约：

现在可以看到合约已经部署到了Block 2。合约已部署到以下地址：

0x1aC3CD1b37898ed4D3005f3C12b4425A6eFFDc30

对于Ganache，我们在端口 8545运行它，并可以通过web.Web()连接到它。然后可以将ABI数据压缩为一个字符串。我们可以使用we3.eth.contract()调用该合约：

import web3

w3 = web3.Web3(web3.HTTPProvider('http://127.0.0.1:8545'))
abi="[{\"inputs\":[{\"internalType\":\"uint256\",\"name\":\"a\",\"type\":\"uint256\"},{\"internalType\":\"uint256\",\"name\":\"b\",\"type\":\"uint256\"}],\"name\":\"add\",\"outputs\":[{\"internalType\":\"uint256\",\"name\":\"\",\"type\":\"uint256\"}],\"stateMutability\":\"view\",\"type\":\"function\"},{\"inputs\":[{\"internalType\":\"uint256\",\"name\":\"a\",\"type\":\"uint256\"},{\"internalType\":\"uint256\",\"name\":\"b\",\"type\":\"uint256\"}],\"name\":\"mul\",\"outputs\":[{\"internalType\":\"uint256\",\"name\":\"\",\"type\":\"uint256\"}],\"stateMutability\":\"view\",\"type\":\"function\"},{\"inputs\":[{\"internalType\":\"uint256\",\"name\":\"a\",\"type\":\"uint256\"}],\"name\":\"sqr\",\"outputs\":[{\"internalType\":\"uint256\",\"name\":\"\",\"type\":\"uint256\"}],\"stateMutability\":\"view\",\"type\":\"function\"},{\"inputs\":[{\"internalType\":\"uint256\",\"name\":\"x\",\"type\":\"uint256\"}],\"name\":\"sqrt\",\"outputs\":[{\"internalType\":\"uint256\",\"name\":\"y\",\"type\":\"uint256\"}],\"stateMutability\":\"view\",\"type\":\"function\"},{\"inputs\":[{\"internalType\":\"uint256\",\"name\":\"a\",\"type\":\"uint256\"},{\"internalType\":\"uint256\",\"name\":\"b\",\"type\":\"uint256\"}],\"name\":\"sub\",\"outputs\":[{\"internalType\":\"uint256\",\"name\":\"\",\"type\":\"uint256\"}],\"stateMutability\":\"view\",\"type\":\"function\"}]"
c = w3.eth.contract(address='0x1aC3CD1b37898ed4D3005f3C12b4425A6eFFDc30', abi=abi)

a=5
b=4

rtn= c.caller().add(a,b)
print(f"{a}+{b}={rtn}")
rtn= c.caller().mul(a,b)
print(f"{a}*{b}={rtn}")
rtn= c.caller().sub(a,b)
print(f"{a}-{b}={rtn}")
rtn= c.caller().sqr(a)
print(f"sqr({a})={rtn}")
rtn= c.caller().sqrt(a)
print(f"sqrt({a})={rtn}")

现在我们可以简单地调用智能合约中的函数，形式如下:

rtn= c.caller().add(a,b)

print(f"{a}+{b}={rtn}")

下面的代码运行示例验证了对智能合约的调用：

% **python web.py**
5+4=9
5*4=20
5-4=1
sqr(5)=25
sqrt(5)=2

我们需要做的就是编译智能合约并部署它，然后记录智能合约和ABI的地址，最后调用智能合约中的功能。

Source：https://medium.com/@billatnapier/calling-smart-contracts-from-python-977a8a9190e2

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