Python – Encoding of headers in MIMEText

emailmime-messagepythonpython-3.x

I'm using MIMEText to create an email from scratch in Python 3.2, and I have trouble creating messages with non-ascii characters in the subject.

For example

from email.mime.text import MIMEText
body = "Some text"
subject = "» My Subject"                   # first char is non-ascii
msg = MIMEText(body,'plain','utf-8')
msg['Subject'] = subject                   # <<< Problem probably here
text = msg.as_string()

The last line gives me the error

UnicodeEncodeError: 'ascii' codec can't encode character '\xbb' in position 0: ordinal not in range(128)

How do I tell MIMEText that the subject is not ascii ? subject.encode('utf-8') doesn't help at all, and anyway I've seen people using unicode strings with no problems in other answers (see for example Python – How to send utf-8 e-mail?)

Edit: I'd like to add that the same code doesn't give any error in Python 2.7 (thought that doesn't mean that the result is correct).

Best Answer

I found the solution. Email headers containing non ascii characters need to be encoded as per RFC 2047. In Python this means using email.header.Header instead of a regular string for header content (see http://docs.python.org/2/library/email.header.html). The right way to write the above example is then

from email.mime.text import MIMEText
from email.header import Header
body = "Some text"
subject = "» My Subject"                   
msg = MIMEText(body,'plain','utf-8')
msg['Subject'] = Header(subject,'utf-8')
text = msg.as_string()

The subject string will be encoded in the email as

=?utf-8?q?=C2=BB_My_Subject?=

The fact the in python 2.x the previous code was working for me is probably related to the mail client being able to interpret the wrongly encoded header.

Related Solutions

Python – Setting the correct encoding when piping stdout in Python

Your code works when run in an script because Python encodes the output to whatever encoding your terminal application is using. If you are piping you must encode it yourself.

A rule of thumb is: Always use Unicode internally. Decode what you receive, and encode what you send.

# -*- coding: utf-8 -*-
print u"åäö".encode('utf-8')

Another didactic example is a Python program to convert between ISO-8859-1 and UTF-8, making everything uppercase in between.

import sys
for line in sys.stdin:
    # Decode what you receive:
    line = line.decode('iso8859-1')

    # Work with Unicode internally:
    line = line.upper()

    # Encode what you send:
    line = line.encode('utf-8')
    sys.stdout.write(line)

Setting the system default encoding is a bad idea, because some modules and libraries you use can rely on the fact it is ASCII. Don't do it.

Python – Writing Unicode text to a text file

Deal exclusively with unicode objects as much as possible by decoding things to unicode objects when you first get them and encoding them as necessary on the way out.

If your string is actually a unicode object, you'll need to convert it to a unicode-encoded string object before writing it to a file:

foo = u'Δ, Й, ק, ‎ م, ๗, あ, 叶, 葉, and 말.'
f = open('test', 'w')
f.write(foo.encode('utf8'))
f.close()

When you read that file again, you'll get a unicode-encoded string that you can decode to a unicode object:

f = file('test', 'r')
print f.read().decode('utf8')

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