python - MIMEText UTF-8 encode problems when sending email

Question

Here is a part of my code which sends an email:

servidor = smtplib.SMTP()
servidor.connect(HOST, PORT)
servidor.login(user, usenha)
assunto = str(self.lineEdit.text())
para = str(globe_email)             
texto = self.textEdit.toPlainText()
textos = str(texto)
corpo = MIMEText(textos.encode('utf-8'), _charset='utf-8')
corpo['From'] = user
corpo['To'] = para
corpo['Subject'] = assunto
servidor.sendmail(user, [para], corpo.as_string())

Everything is ok except the part of the Subject. When I try to send a string with special characters (e.g. "a??o") it raises this error:

UnicodeEncodeError: 'ascii' codec can't encode characters in position 1-2: ordinal not in range(128)

How can I send emails with special characters in the Subject of MIMEText?

Answer 1

It seems that, in python3, a Header object is needed to encode a Subject as utf-8:

# -*- coding: utf-8 -*-
from email.mime.text import MIMEText
from email.header import Header
s = 'a??o'
m = MIMEText(s, 'plain', 'utf-8')
m['Subject'] = Header(s, 'utf-8')
print(repr(m.as_string()))

Output:

'Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Subject: =?utf-8?b?YcOnw6Nv?=

YcOnw6Nv

So the original script would become:

servidor = smtplib.SMTP()
servidor.connect(HOST, PORT)
servidor.login(user, usenha)
assunto = str(self.lineEdit.text())
para = str(globe_email)             
texto = str(self.textEdit.toPlainText())
corpo = MIMEText(texto, 'plain', 'utf-8')
corpo['From'] = user
corpo['To'] = para
corpo['Subject'] = Header(assunto, 'utf-8')
servidor.sendmail(user, [para], corpo.as_string())