create html email out of zope template and compute txt version using

mail.py

# for information how to use a zope page template to rende the html see
# https://github.com/collective/collective.dancing/blob/1.0.1/collective/dancing/composer.py#L342

from Products.CMFPlone.utils import safe_unicode
from email.Header import Header
from email.MIMEMultipart import MIMEMultipart
from email.MIMEText import MIMEText
from email.Utils import formatdate
import email
import html2text


def create_html_mail(subject, html, text=None, from_addr=None, to_addr=None,
                     headers=None, encoding='UTF-8'):
    """Create a mime-message that will render HTML in popular
    MUAs, text in better ones.

    adapted collective.singing standard to strip style definitions off the
    plain text version
    """
    html = html.encode(encoding)
    if text is None:
        # Produce an approximate textual rendering of the HTML string,
        # unless you have been given a better version as an argument

        # see tests/test_newsletterformatter for configuration options
        parser = html2text.HTML2Text()
        # for images, simply show their alt-text
        parser.ignore_images = False
        parser.images_to_alt = True
        # skip links to named anchors
        parser.skip_internal_links = True
        # if link text and href is the same, simply show link
        parser.use_automatic_links = True
        # protect links from linebreaks - looks good for emails
        parser.protect_links = True
        # true to show links next to their text content
        parser.inline_links = True
        text = parser.handle(safe_unicode(html))
    else:
        text = text.encode(encoding)

    # if we would like to include images in future, there should
    # probably be 'related' instead of 'mixed'
    msg = MIMEMultipart('mixed')
    # TODO: maybe later :)
    # msg['From'] = Header("%s <%s>" % (send_from_name, send_from), encoding)
    msg['Subject'] = Header(subject, encoding)
    msg['From'] = from_addr
    msg['To'] = to_addr
    msg['Date'] = formatdate(localtime=True)
    msg["Message-ID"] = email.Utils.make_msgid()
    if headers:
        for key, value in headers.items():
            msg[key] = value
    msg.preamble = 'This is a multi-part message in MIME format.'

    alternatives = MIMEMultipart('alternative')
    msg.attach(alternatives)
    alternatives.attach(MIMEText(text, 'plain', _charset=encoding))
    alternatives.attach(MIMEText(html, 'html', _charset=encoding))

    return msg