Jinja policies in Django projects

Jinja policies are used to set the global behavior of Jinja built-in filters and other template constructs. Jinja policies are set in Jinja environments -- just like Jinja globals in listing 4-11 or custom Jinja filters & tests in listing 4-25.

For example, you can use Jinja policies to alter the way the json or urlize built-in filters operate by default. Listing 4-30 illustrates a custom Jinja environment that alters the Jinja built-in truncate filter and sets the leeway option to 0.

Listing 4-30 Custom Jinja environment with policies

from jinja2.environment import Environment
from coffeehouse.jinja.filters import customcoffee, squarerootintext, startswithvowel
class JinjaEnvironment(Environment):
    def __init__(self,**kwargs):
        super(JinjaEnvironment, self).__init__(**kwargs)
        self.policies['truncate.leeway'] = 0

As you can see in listing 4-30, to register Jinja policies you access self.policies and assign it the policy key name[8] -- in this case corresponding to truncate.leeway -- along with the policy value -- in this case corresponding to 0. By setting the Jinja policy in listing 4-30, anytime you use the truncate filter in Jinja templates, the leeway is set to 0, instead of the default 5.

  1. http://jinja.pocoo.org/docs/2.9/api/#policies