def render_jinja2_block(template_name, extra_vars=None, block=None, cache_key=None, cache_type=None, cache_expire=None):
    """Render a template or a block from template with Jinja2

    Accepts the cache options ``cache_key``, ``cache_type``, and ``cache_expire``.

    Allows rendering of single block from the template:

        # In controller
        return render('/controller/index.html', block='sidebar')

    """
    from pylons.templating import pylons_globals, cached_template
    from webhelpers.html import literal
    from jinja2.utils import concat

    # Create a render callable for the cache function
    def render_template():
        # Pull in extra vars if needed
        globs = extra_vars or {}

        # Second, get the globals
        globs.update(pylons_globals())

        # Grab a template reference
        template = \
                globs['app_globals'].jinja2_env.get_template(template_name)

        # Determine render function depending on whether block
        # is defined or not and fallback to full template if
        # block is defined but not found in template
        # TBD: maybe we should throw when block is defined but not found?
        render_func = template.blocks.get(block, template.root_render_func) if block else template.root_render_func

        try:
            return literal(concat(render_func(template.new_context(globs))))
        except:
            from jinja2.debug import translate_exception
            exc_type, exc_value, tb = translate_exception(sys.exc_info())
            raise exc_type, exc_value, tb

    return cached_template(template_name, render_template, cache_key=cache_key, cache_type=cache_type, cache_expire=cache_expire)