python - How can a custom jinja2 tag interface with the context of a flask request -

i'm writing custom jinja2 extension use in flask applications , i'm looking way access templates context data using tag i'm implementing. is, want extension tag use context params passed template:

@app.route('/users/<user_id>') def user_page(user_id):     ...     return render_template('users/index.html', user_id=user_id, active=true) 

the template:

<!-- want tag see value of user_id , active --> {% my_jinja2_tag %} 

i know can render context variable using {{ user_id }}, i'm looking way inspect context of template rendering custom jinja2 extension. doable? thanks.

contextreference

yes, it's possible using jinja2.nodes.contextreference(). see api reference here.

relax, i'm going guide through it. :)

first extension:

class activecheckerextension(jinja2.ext.extension):     """     give {% check_active %} tag.     """      template = 'active : %s'     tags = set(['check_active'])      def _render_tag(self, context, caller):         return jinja2.markup(self.template % unicode(context['active']))      def parse(self, parser):         ctx_ref = jinja2.nodes.contextreference()         lineno = next(parser.stream).lineno         node = self.call_method('_render_tag', [ctx_ref], lineno=lineno)         return jinja2.nodes.callblock(node, [], [], [], lineno=lineno) 

then let's add flask's jinja2.

app.jinja_env.add_extension(activecheckerextension) 

now in template, can do:

{% check_active %} 

make sure active defined in templates add tag to, or else you'll keyerror because context won't have template variable.