python - Encode MIMEText as quoted printables

Question

Python supports a quite functional MIME-Library called email.mime.

What I want to achieve is to get a MIME Part containing plain UTF-8 text to be encoded as quoted printables and not as base64. Although all functionallity is available in the library, I did not manage to use it:

Example:

import email.mime.text, email.encoders
m=email.mime.text.MIMEText(u'This is the text containing ünic?de', _charset='utf-8')
m.as_string()
# => Leads to a base64-encoded message, as base64 is the default.

email.encoders.encode_quopri(m)
m.as_string()
# => Leads to a strange message

The last command leads to a strange message:

Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Content-Transfer-Encoding: quoted-printable

GhpcyBpcyB0aGUgdGV4dCBjb250YWluaW5nIMO8bmljw7ZkZQ=3D=3D

This is obviously not encoded as quoted printables, the double transfer-encoding header is strange at last (if not illegal).

How can I get my text encoded as quoted printables in the mime-message?

Answer 1

Okay, I got one solution which is very hacky, but at least it leads into some direction: MIMEText assumes base64 and I don't know how to change this. For this reason I use MIMENonMultipart:

import email.mime, email.mime.nonmultipart, email.charset
m=email.mime.nonmultipart.MIMENonMultipart('text', 'plain', charset='utf-8')

#Construct a new charset which uses Quoted Printables (base64 is default)
cs=email.charset.Charset('utf-8')
cs.body_encoding = email.charset.QP

#Now set the content using the new charset
m.set_payload(u'This is the text containing ünic?de', charset=cs)

Now the message seems to be encoded correctly:

Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable

This is the text containing =C3=BCnic=C3=B6de

One can even construct a new class which hides the complexity:

class MIMEUTF8QPText(email.mime.nonmultipart.MIMENonMultipart):
  def __init__(self, payload):
    email.mime.nonmultipart.MIMENonMultipart.__init__(self, 'text', 'plain',
                                                      charset='utf-8')

    utf8qp=email.charset.Charset('utf-8')
    utf8qp.body_encoding=email.charset.QP

    self.set_payload(payload, charset=utf8qp) 

And use it like this:

m = MIMEUTF8QPText(u'This is the text containing ünic?de')
m.as_string()