[Grok-dev] grokcore.resource

Danilo G B danilogbotelho at yahoo.com
Tue May 1 23:03:41 UTC 2012

I'd suggest another name for the directive like 'resources' (in the plural, as with 'permissions').

'includes' is probably too generic but makes a lot of sense to me.

Also, why include parents' resources for subclasses as the default behaviour? How to turn that off? I usually subclass layouts to change the needed resources. So, I'd suggest extending the 'resources' directive to have it accept resources and 'resource includers':

class Layout1(grok.Layout):
    grok.resources(r1, r2)

class Layout2(Layout1):
    grok.resources(Layout1, r3)

"In order to make this work for Layouts I don't see another way than
emitting an event right before the layout is rendered in

I haven't checked this, but can't you get the layout from the view being traversed to?

Maybe a solution which adds a method to the 'resource includers' makes this more easy and natural. I haven't thought this through. Lately I've been using a method named update_resources called from my layouts which is responsible for updating the resources required by each view. This allows for subclasses to decide whether use parents resources or not.

I hope we can reach an easy to use and natural way of including resources in Grok.


Message: 3
Date: Tue, 1 May 2012 10:42:56 +0200
From: Jan-Jaap Driessen <jdriessen at minddistrict.com>
To: Grok <grok-dev at zope.org>
Subject: [Grok-dev] grokcore.resource
    <CABk+M0B_rA+e7-aKFyWqY13EUDW4r0RbUb8qmj+x6ZtjpN14-g at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

In the train back home from the grok sprint yesterday I took some
parts of megrok.resource [1] to combine with fanstatic [2] into
grokcore.resource [3].

With grokcore.resource you can make resources part of your View classes like so:

class MyView(grok.View):
    grokcore.resource.include(css_a, css_b)

This is a handsome replacement of the "old" way of declaring resource,
often in the update method of the view:

    def update(self):

(This "old" way is still supported.)

The "include" directive code looks like this:

class include(martian.Directive):
    scope = martian.CLASS
    store = martian.MULTIPLE
    validate = validateInclusion

    def factory(self, *resources):
            _resources_advice, depth=3)
        return resources

def _resources_advice(cls):
    if include.bind().get(cls):
        if not grokcore.resource.interfaces.IResourcesIncluder.implementedBy(
    return cls

The result of using the "include" directive is that the class which it
is used on will be marked with a marker interface
We add an event listener for IBeforeTraverseEvent that will listen to
this interface and will need the resources at that time::

def handle_inclusion(includer, event):
    includer = zope.security.proxy.removeSecurityProxy(includer)
    needs = set()
    # XXX Need to fix this?
    for class_ in includer.__class__.__mro__:
        if grokcore.resource.interfaces.IResourcesIncluder.implementedBy(class_):
            father = zope.security.proxy.removeSecurityProxy(class_)
            for resources in \
    for resource in needs:

I am not sure whether there is a smarter way of finding all resources
needed by a View if this View subclasses from another View. Maybe it
is just my limited understanding of how martian works. I need a second
pair of eyes here.

At this point, we can use grokcore.resource for grok.View classes, but
not yet for viewlets and on layouts (grokcore.layout).

In the zope.viewlet code, a BeforeUpdateEvent is sent, which we
subscribe to in grokcore.resource and need the resources for viewlets:

def handle_inclusion(includer, event):
    # Same inclusion code as before.

In order to make this work for Layouts I don't see another way than
emitting an event right before the layout is rendered in

def __call__(self, view):
    self.view = view
    zope.event.notify(BeforeUpdateEvent(self, self.request))
    return self.render()

Is this OK? We could make the event grokcore.layout specific of course.

I would appreciate your feedback on the questions above. Afterwards, I
can finish grokcore.resource (readme, tests for viewlet/layout) and
would like to integrate the directive in grok (the package) under the
name 'resource', so you can write:

class MyView(grok.View):
    grok.resource(css_a, css_b)

Thanks for reading this far,


1) http://pypi.python.org/pypi/megrok.resource/0.5
2) http://fanstatic.org
3) http://svn.zope.org/grokcore.resource/trunk/


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