如何附加smtplib文件？

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.application import MIMEApplication

# 创建邮件对象
msg = MIMEMultipart()
msg['From'] = 'sender@example.com'
msg['To'] = 'receiver@example.com'
msg['Subject'] = '附件示例邮件'

# 添加邮件正文
body = MIMEText('这是一封带附件的示例邮件。')
msg.attach(body)

# 添加附件
with open('path/to/attachment.pdf', 'rb') as attachment:
    part = MIMEApplication(attachment.read())
    part.add_header('Content-Disposition', 'attachment', filename='attachment.pdf')
    msg.attach(part)

# 发送邮件
smtp_server = 'smtp.example.com'
smtp_port = 587
smtp_username = 'your_username'
smtp_password = 'your_password'

with smtplib.SMTP(smtp_server, smtp_port) as server:
    server.starttls()
    server.login(smtp_username, smtp_password)
    server.send_message(msg)