Every boilerplate project and tutorial I have found for Flask on GAE includes a separate version of Jinja2, but GAE Python 2.7 includes Jinja2 2.6 by default and including it in app.yaml is much more convenient:
libraries:
- name: jinja2
version: 2.6
Are there any advantages of including a separate version of Jinja2 instead of using the GAE version?
Not really, no. I mean, if you wanted a version of
jinja2that isn’t available on AppEngine, you could include it custom, but as long as you’re not picky about versions, just use what’s already available.