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.