why decorate Jinja2 instances with @webapp2.cached_property

Question

The webapp2 site (http://webapp-improved.appspot.com/api/webapp2_extras/jinja2.html) has a tutorial on how to use webapp2_extras.jinja2, and the code is below.

My question is: why cache the webapp2_extras.jinja2.Jinja2 instance return by return jinja2.get_jinja2(app=self.app)? I checked the code of @webapp2.cached_property and found that it caches the Jinja2 instance in a instance of BaseHandler, which will be destroyed after the request, so why bother to cache it? Did I miss something here?

import webapp2

from webapp2_extras import jinja2

class BaseHandler(webapp2.RequestHandler):

    @webapp2.cached_property
    def jinja2(self):
        # Returns a Jinja2 renderer cached in the app registry.
        return jinja2.get_jinja2(app=self.app)

    def render_response(self, _template, **context):
        # Renders a template and writes the result to the response.
        rv = self.jinja2.render_template(_template, **context)
        self.response.write(rv)

Answer 1

Here you can find the documentation about cached_property.

The BaseHandler class will be later on called often. My understanding is that to avoid the overhead of calling jinja2.get_jinja2(app=self.app) each time, such reference is evaluated the first time only, and then returned many times later on, i.e. every time a view is called.

To see this happen in code, see this example, where each view is derived from the same BaseHandler class.