如何模拟NpgsqlTransaction和NpgsqlConnection？

class MyTransaction:
    def __init__(self, connection):
        self.connection = connection
        self.is_committed = False

    def commit(self):
        if not self.is_committed:
            # 执行事务提交的逻辑
            self.connection.commit()
            self.is_committed = True

    def rollback(self):
        if not self.is_committed:
            # 执行事务回滚的逻辑
            self.connection.rollback()
            self.is_committed = True

class MyConnection:
    def __init__(self, connection_string):
        self.connection_string = connection_string

    def open(self):
        # 执行与数据库建立连接的逻辑
        print("连接已打开")

    def close(self):
        # 执行与数据库关闭连接的逻辑
        print("连接已关闭")

    def commit(self):
        # 执行事务提交的逻辑
        print("事务已提交")

    def rollback(self):
        # 执行事务回滚的逻辑
        print("事务已回滚")