请写一个python语言的pbft

PBFT（Practical Byzantine Fault Tolerance）是一种拜占庭容错算法，用于解决分布式系统中存在的拜占庭故障问题。下面是一个简单的 Python 代码实现 PBFT 算法：

import hashlib
import json
import socket
import time


class PBFTNode:
    def __init__(self, node_id, nodes):
        self.node_id = node_id
        self.nodes = nodes
        self.seq_num = 0
        self.state = "IDLE"
        self.view = 0
        self.log = []

    def start(self):
        server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        server_socket.bind(("localhost", self.node_id))
        server_socket.listen(1)
        while True:
            client_socket, address = server_socket.accept()
            message = client_socket.recv(1024).decode()
            message = json.loads(message)
            print("Received Message: {}".format(message))
            if message["type"] == "PRE-prepare":
                self.pre_prepare(message)
            elif message["type"] == "prepare":
                self.prepare(message)
            elif message["type"] == "commit":
                self.commit(message)

    def pre_prepare(self, message):
        if self.state == "IDLE":
            self.seq_num += 1
            self.state = "PRE-PREPARE"
            self.view = message["view"]
            self.log.append(message)
            signature = self.sign(message)
            pre_prepare_message = {
                "type": "PREPARE",
                "seq_num": self.seq_num,
                "view": self.view,
                "digest": message["digest"],
                "signature": signature,
                "node_id": self.node_id
            }
            for node in self.nodes:
                if node != self.node_id:
                    self.send_message(node, pre_prepare_message)

    def prepare(self, message):
        if self.state == "PRE-PREPARE" and message["seq_num"] == self.seq_num and message["view"] == self.view:
            self.log.append(message)
            if len(self.log) == 2 * len(self.nodes) - 1:
                self.state = "PREPARED"
                commit_message = {
                    "type": "COMMIT",
                    "seq_num": self.seq_num,
                    "view": self.view,
                    "digest": message["digest"],
                    "node_id": self.node_id
                }
                for node in self.nodes:
                    if node != self.node_id:
                        self.send_message(node, commit_message)

    def commit(self, message):
        if self.state == "PREPARED" and message["seq_num"] == self.seq_num and message["view"] == self.view:
            self.log.append(message)
            if len(self.log) == 2 * len(self.nodes) - 1:
                self.state = "IDLE"
                print("Transaction committed: {}".format(message["digest"]))

    def sign(self, message):
        message_str = json.dumps(message, sort_keys=True).encode()
        return hashlib.sha256(message_str).hexdigest()

    def send_message(self, node_id, message):
        client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        client_socket.connect(("localhost", node_id))
        message_str = json.dumps(message).encode()
        client_socket.sendall(message_str)
        client_socket.close()


if __name__ == "__main__":
    nodes = [8000, 8001, 8002]
    pbft_nodes = [PBFTNode(node_id, nodes) for node_id in nodes]
    for pbft_node in pbft_nodes:
        pbft_node.start()

这个 PBFT 实现中，我们创建了一个名为 PBFTNode 的类，代表一个 PBFT 节点。在 start 方法中，我们创建了一个 TCP 服务器套接字以监听来自其他节点的消息。当我们收到消息时，我们根据消息类型调用不同的方法：pre_prepare、prepare 或 commit。在 pre_prepare 方法中，我们根据收到的消息创建了一条新的日志记录，并向其他节点发送了 PREPARE 消息。在 prepare 方法中，我们检查是否收到了足够的 PREPARE 消息，如果是，则发送 COMMIT 消息。在 commit 方法中，我们检查是否收到了足够的 COMMIT 消息，如果是，则提交事务。

在主程序中，我们创建了三个节点并启动它们，每个节点都监听来自其他节点的消息。当一个节点接收到消息时，它将根据消息类型调用适当的方法来处理该消息。