class Nl2BrExtension(markdown.Extension):

    def extendMarkdown(self, md, md_globals):
        br_tag = markdown.inlinepatterns.SubstituteTagPattern(BR_RE, 'br')
md.inlinePatterns.add('nl', br_tag, '_end')

def makeExtension(configs=None):
    return Nl2BrExtension(configs)
How do I make django's markdown filter transform a carriage return to <br />?