python send messages, download attachments Chinese garbage problem solution

Solution:

import base64

part = MIMEText(open(fileName, 'rb').read(), 'base64', 'UTF-8')
part["Content-Type"] = 'application/octet-stream'
part.add_header('Content-Disposition', 'attachment', filename= '=?utf-8?b?' + base64.b64encode(fileName.encode('UTF-8')) + '?=')

然后，中文显示正常！！！