Django Text/HTML message with inline images

messages.py

# coding: utf-8


import os
import re
import posixpath
import email.charset

from email.mime.image import MIMEImage
from urllib.parse import unquote

from django.conf import settings
from django.core.mail import SafeMIMEMultipart, SafeMIMEText, EmailMultiAlternatives
from django.template import loader, RequestContext, TemplateDoesNotExist
from django.contrib.staticfiles import finders
from django.template.loader import render_to_string

INLINE_SCHEME = re.compile(r' src="inline://(?P<path>.*?)" ?', re.MULTILINE)

DEFAULT_CHARSET = "utf-8"

email.charset.add_charset(DEFAULT_CHARSET, email.charset.SHORTEST, None, None)


class HTMLMessage(object):
    def __init__(self, from_, to_, subject_template, text_template_name, html_template_name, context):
        self.from_ = from_
        self.to_ = to_

        subject = loader.render_to_string(subject_template, context)
        self.subject = ''.join(subject.splitlines())

        context.update({"subject": subject})
        self.context = context

        self.text = loader.render_to_string(text_template_name, context)
        self.html = loader.render_to_string(html_template_name, context)

    def message(self):
        mail = SafeMIMEMultipart("related")
        mail.preamble = "This is a multi-part message in MIME format."

        mail["Subject"] = self.subject
        mail["From"] = self.from_
        mail["To"] = self.to_

        paths = []

        def repl(match):
            paths.append(match.group("path"))
            return ' src="cid:image-%05d" ' % (len(paths),)

        html = re.sub(INLINE_SCHEME, repl, self.html)

        alternative = SafeMIMEMultipart("alternative")
        alternative.attach(SafeMIMEText(self.text, "plain", _charset=DEFAULT_CHARSET))
        alternative.attach(SafeMIMEText(html, "html", _charset=DEFAULT_CHARSET))
        mail.attach(alternative)

        for index, path in enumerate(paths):
            path = path.strip()
            if path.startswith(settings.STATIC_URL):
                path = path[len(settings.STATIC_URL):]

            path = posixpath.normpath(unquote(path)).lstrip('/')

            if settings.DEBUG:
                resolved_path = finders.find(path)
            else:
                resolved_path = os.path.join(settings.STATIC_ROOT, path)

            with open(resolved_path, "rb") as fp:
                image = MIMEImage(fp.read())

            image.add_header('Content-ID', '<image-%05d>' % (index + 1))
            mail.attach(image)

        return mail