Markdown rendering in Chameleon

markdown.py

# This module allows you to use markdown in Chameleon templates from pyramid.
#
# Markdown rendering is only down for text that is translatable, and has its
# message context set to ``markdown``. This is a complete abuse of the translation
# system, but currently provides the simplest way to get markdown running in
# Chameleon.
import CommonMark
from chameleon.utils import Markup
from translationstring import ChameleonTranslate
from pyramid_chameleon.localization import translator
from pyramid_chameleon.interfaces import IChameleonTranslate


def render_markdown(source):
    parser = CommonMark.DocParser()
    renderer = CommonMark.HTMLRenderer()
    ast = parser.parse(source)
    return Markup(renderer.render(ast))


def MarkdownTranslator(translator):
    org_translate = ChameleonTranslate(translator)

    def translate(msgid, domain=None, mapping=None, context=None,
             target_language=None, default=None):
        tr = org_translate(msgid, domain, mapping, context, target_language, default)
        if context == 'markdown':
            tr = render_markdown(tr)
        return tr

    return translate


def setup_markdown_translations(registry):
    mdtranslate = MarkdownTranslator(translator)
    registry.registerUtility(mdtranslate, IChameleonTranslate)


def includeme(config):  # pragma: no cover
    config.action(None,
        callable=setup_markdown_translations, args=(config.registry,),
        order=1200)  # Order after pyramid_chameleon.localization

Why not implement an expression type instead?

{{ markdown: some_dynamic_markdown_string }}
{{ markdown: string: ### Heading }}