Encoding mail subject (SMTP) in Python with non-ASCII characters

I am using Python module MimeWriter to construct a message and smtplib to send a mail constructed message is:

file msg.txt:
-----------------------
Content-Type: multipart/mixed;
from: me<me@abc.com>
to: me@abc.com
subject: 主題

Content-Type: text/plain;charset=utf-8

主題

I use the code below to send a mail:

import smtplib
s=smtplib.SMTP('smtp.abc.com')
toList = ['me@abc.com']
f=open('msg.txt') #above msg in msg.txt file
msg=f.read()
f.close()
s.sendmail('me@abc.com',toList,msg)

I get mail body correctly but subject is not proper,

subject: some junk characters

主題        开发者_开发技巧   <- body is correct.

Please suggest? Is there any way to specify the decoding to be used for the subject also, as being specified for the body. How can I get the subject decoded correctly?

From http://docs.python.org/library/email.header.html

from email.message import Message
from email.header import Header
msg = Message()
msg['Subject'] = Header('主題', 'utf-8')
print msg.as_string()

Subject: =?utf-8?b?5Li76aGM?=

more simple:

from email.header import Header
print Header('主題', 'utf-8').encode()

=?utf-8?b?5Li76aGM?=

as complement decode may made with:

from email.header import decode_header
a = decode_header("""=?utf-8?b?5Li76aGM?=""")[0]
print(a[0].decode(a[1]))

Reference: Python - email header decoding UTF-8

The subject is transmitted as an SMTP header, and they are required to be ASCII-only. To support encodings in the subject you need to prefix the subject with whatever encoding you want to use. In your case, I would suggest prefix the subject with ?UTF-8?B? which means UTF-8, Base64 encoded.

In other words, I believe your subject header should more or less look like this:

Subject: =?UTF-8?B?JiMyMDAyNzsmIzM4OTg4Ow=?=

In PHP you could go about it like this:

// Convert subject to base64
$subject_base64 = base64_encode($subject);
fwrite($smtp, "Subject: =?UTF-8?B?{$subject_base64}?=\r\n");

In Python:

import base64
subject_base64 = base64.encodestring(subject).strip()
subject_line = "Subject: =?UTF-8?B?%s?=" % subject_base64

In short, if you use the EmailMessage API, you should code like this:

from email.message import EmailMessage
from email.header import Header
msg = EmailMessage()
msg['Subject'] = Header('主題', 'utf-8').encode()

Answer from @Sérgio cannot be used in the EmailMessage API, cause only string object can be assigned to EmailMessage()["Subject"], but not an email.header.Header object.