尝试发送电子邮件附件时出错

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.base import MIMEBase
from email import encoders

# 配置SMTP服务器信息
smtp_server = 'smtp.example.com'
smtp_port = 587
smtp_username = 'your_email@example.com'
smtp_password = 'your_password'

# 创建邮件对象
msg = MIMEMultipart()
msg['From'] = smtp_username
msg['To'] = 'recipient@example.com'
msg['Subject'] = 'Test Email with Attachment'

# 添加邮件正文
body = 'This is a test email with an attachment.'
msg.attach(MIMEText(body, 'plain'))

# 添加附件
filename = 'example.txt'
attachment = open(filename, 'rb')

part = MIMEBase('application', 'octet-stream')
part.set_payload((attachment).read())
encoders.encode_base64(part)
part.add_header('Content-Disposition', "attachment; filename= %s" % filename)
msg.attach(part)

# 连接SMTP服务器并发送邮件
server = smtplib.SMTP(smtp_server, smtp_port)
server.starttls()
server.login(smtp_username, smtp_password)
text = msg.as_string()
server.sendmail(smtp_username, 'recipient@example.com', text)
server.quit()