Jinja

Global objects

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This section covers the behavior of global objects in the Jinja namespace and also the behavior of their attributes.

Functions

Filters and Tests are special kind of functions you cannot call without and argument. Global functions are different. Those are really just ordinary python functions. You can register them on the global namespace easily:

def my_function():
    return [1, 2, 3]

env.globals['my_function'] = my_function

In the template you can not call it like this:

{{ my_function() }}

Of couse you can pass any argument to it. But what if you want to access the context or environment? In that case you have to decorate a function or mark it (both work exactly the same, but the decorator way is probably nicer if you have python >= 2.4):

from cgi import escape
from pprint import pformat
from jinja.datastructure import contextcallable

@contextcallable
def printcontext(env, context):
    result = []
    for key, value in context.to_dict():
        result.append('<tr><th>%s</th><td>%r</td></tr>' %
                      (escape(unicode(key)), escape(pformat(value))))
    return '<table>%s</table>' % u'\n'.join(result)

If this function is registered in the environment namespace then and called from the template it should return the content of the context as simple html template. Of course you can modify the context too. For more informations about the context object have a look at the context object documentation.

Deferred Values

You can pass functions to the template that are called to provide values at first access. Say you want to pass the list of recently written comments to all templates. But not necessarily every template will render that. In that situation you can create a function that returns that value and wrap it in an Deferred object. The first time a template accesses the variable then the Deferred object is resolved:

from jinja.datastructure import Deferred
from yourapplication.models import Comments

def get_recent_comments(env, context, name):
    # do what ever you want here.
    return Comments.get_recent(10)

env.globals['recent_comments'] = Deferred(get_recent_comments)

The function is always called with the same arguments. The first one is the current environment, the second the context and the third is the name of the variable. In this example recent_comments.

Unsafe Methods / Attributes

Because Jinja is sandboxed it provides several ways to prevent unsafe attribute access. You can mark both attributes and methods as unsafe:

from jinja.datastructure import unsafe

class MyModel(...):

    # just give access to a and b. Default is all
    # note that this also disallows the functions from below.
    # if you use jinja_allowed_attributes you don't have to
    # do the code below because methods are threaded as attributes
    # too.
    jinja_allowed_attributes = ['a', 'b']

    def __init__(self, ...):
        ...
        self.a = ...
        self.b = ...

    # python2.4 way of marking methods
    @unsafe
    def save(self):
        """Save the model."""

    # python2.3 way for the same
    def delete(self):
        """Delete the model."""
    delete.jinja_unsafe_call = True