向 EmailMessage 添加附件会引发 TypeError：set_text_content() 得到了意外的关键字参数“maintype”

Question

按照Python 电子邮件示例中的示例，添加附件似乎应该非常简单。但是，以下方法不起作用：

import smtplib
from email.message import EmailMessage
import json

# Initialize message.
msg = EmailMessage()
msg['Subject'] = 'Testing, testing 1-2-3'
msg['To'] = 'fake@example.com'
msg['From'] = 'extrafake@example.com'
msg.set_content('Trying to attach a .json file')

# Create json attachment.
attachment = json.dumps({'This': 'is json'})

# Attempt to attach. This raises an exception.
msg.add_attachment(attachment, maintype='application', subtype='json', filename='test.json')

这是例外：

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/usr/local/lib/python3.7/email/message.py", line 1147, in add_attachment
    self._add_multipart('mixed', *args, _disp='attachment', **kw)
  File "/usr/local/lib/python3.7/email/message.py", line 1135, in _add_multipart
    part.set_content(*args, **kw)
  File "/usr/local/lib/python3.7/email/message.py", line 1162, in set_content
    super().set_content(*args, **kw)
  File "/usr/local/lib/python3.7/email/message.py", line 1092, in set_content
    content_manager.set_content(self, *args, **kw)
  File "/usr/local/lib/python3.7/email/contentmanager.py", line 37, in set_content
    handler(msg, obj, *args, **kw)
TypeError: set_text_content() got an unexpected keyword argument 'maintype'

请注意，这非常接近此处的第三个示例，但失败了。知道如何附加json文件吗？

另请注意，此答案提出了类似的工作流程，但使用相同的参数调用相同的函数，因此没有解决我的问题。

Answer 1

EmailMessage.set_content委托给ContentManager，作为参数传递或默认raw_data_manager。

maintype如果内容为bytes，raw_data_manager.set_content接受一个参数，但如果内容为则不接受str。

所以解决方案是将一个bytes实例传递给EmailMessage.set_content：

# Create json attachment.
attachment = json.dumps({'This': 'is json'})

# Encode to bytes
bs = attachment.encode('utf-8')

# Attach
msg.add_attachment(bs, maintype='application', subtype='json', filename='test.json')