如何将用户添加的新项目保存到dat文件中？

import pickle

class Project:
    def __init__(self, name, description, created_at):
        self.name = name
        self.description = description
        self.created_at = created_at

# 创建一个空的项目列表
projects = []

# 添加新项目
def add_project(name, description):
    project = Project(name, description, datetime.now())
    projects.append(project)

# 保存项目到dat文件
def save_projects():
    with open('projects.dat', 'wb') as file:
        pickle.dump(projects, file)

# 从dat文件中加载项目
def load_projects():
    try:
        with open('projects.dat', 'rb') as file:
            projects = pickle.load(file)
    except FileNotFoundError:
        projects = []

# 示例使用
add_project('Project 1', 'This is project 1')
add_project('Project 2', 'This is project 2')
save_projects()
load_projects()

# 打印项目列表
for project in projects:
    print(project.name, project.description, project.created_at)