Flask is amazing. The templating system called jinja2 packed with it is equally amazing.
The default behaviour of flask app is to look for template files specified in app.template_folder directory. Although this will work in most use-cases, sometimes you need additional control over this - for example if you have user specific templates or if you want to load templates from a database, dynamically.
This can be accomplished, by initialising app.jinja_loader with a custom Loader.
Jinja2 ships with serveral different loaders by default. The easiest one is DictLoader, which simply loads tempalte sfrom a dictionary.
from flask import Flask
import jinja2
app = Flask(__name__)
app.jinja_loader = jinja2.DictLoader({
'index.html' : """
{% extends 'base.html' %}
{% block text %}
Super cool!
{% endblock %}
""",
'base.html' : """
<b>{{ self.text() }}</b>
"""
})
@app.route('/')
def doHome():
return render_template('index.html')
The above example was fairly simple - it still pre-loads all templates. If there is a non-trivial requirement where you want to load them from database, then you can use FunctionLoader
def load_template(template_name):
is_uptodate = True
if template_name == 'index.html':
return ("""
{% extends 'base.html' %}
{% block text %}
Super cool!
{% endblock %}
""", None, is_uptodate)
if template_name == 'base.html':
return ("""
<b>{{ self.text() }}</b>
""", None, is_uptodate)
app.jinja_loader = jinja2.FunctionLoader(load_template)
Jinja2 ships with the following loaders, all of which can be used with flask
- FileSystemLoader
- PackageLoader
- DictLoader
- FunctionLoader
- PrefixLoader
- ChoiceLoader
- ModuleLoader