import jinja2
import jinja2.ext
import markdown2

class Markdown2Extension(jinja2.ext.Extension):
    tags = set(['markdown2'])

    def __init__(self, environment):
        super(Markdown2Extension, self).__init__(environment)
        environment.extend(
            markdowner=markdown2.Markdown()
        )   

    def parse(self, parser):
        lineno = parser.stream.next().lineno
        body = parser.parse_statements(
            ['name:endmarkdown2'],
            drop_needle=True
        )
        return jinja2.nodes.CallBlock(
            self.call_method('_markdown_support'),
            [],
            [],
            body
        ).set_lineno(lineno)

    def _markdown_support(self, caller):
        return self.environment.markdowner.convert(caller()).strip()

env = jinja2.Environment(extensions=[Markdown2Extension])

text = """ 
{% markdown2 %}
Hello World
===========

 1. One
 2. {{ two }}
 3. Three
{% endmarkdown2 %}
"""

html = env.from_string(text).render(two='Two')

print html

Which would result in the following output:

<h1>Hello World</h1>

<ol>
<li>One</li>
<li>Two</li>
<li>Three</li>
</ol>