Custom template folders with Flask

Someone was asking on Flask‘s IRC channel #pocoo about sharing templates across more than one app but allowing each app to override the templates (pretty much what Django’s TEMPLATE_DIRS setting is for). One way of doing this would be to customise the Jinja2 template loader.

Here’s a trivial Flask app that searches for templates first in the default folder (‘templates’ in the same folder as the app) and then in an extra folder.

import flask
import jinja2

app = flask.Flask(__name__)
my_loader = jinja2.ChoiceLoader([
    app.jinja_loader,
    jinja2.FileSystemLoader('/path/to/extra/templates'),
])
app.jinja_loader = my_loader

@app.route('/')
def home():
    return flask.render_template('home.html')

if __name__ == "__main__":
    app.run()

The only thing special here is creating a new template loader and then assigning it to the jinja_loader attribute on the Flask application. ChoiceLoader will search for a named template in the order of the loaders, stopping on the first match. In this example I re-used the loader that is created by default for an app, which is roughly like FileSystemLoader('/path/to/app/templates'). There are all kinds of other exciting template loaders available.

I really like the fact that Flask and Bottle’s APIs are so similar. Next I want Flask to include Bottle’s template wrapping decorator by default (there’s a recipe in the Flask docs) and for both of them to re-name it @template.