On Tue, Oct 19, 2004 at 12:10:37PM -0700, David Reid wrote:

On Tue, 2004-10-19 at 02:51, Andrew Bennetts wrote:

...

TAL does allow this, in two ways (that I know of):

First, there's the hackish way:

They're both hackish ways in my opinion, and the latter Another alternative is for the alternative syntax to not even support such behavior, and only be for the general case which would look something like this:

<a nevow:attributes="href=link alt=label"><nevow:slot name="label" /></a>

(Looks an aweful lot like mg's attr.tac example, doesn't it?)

Firstly, I really don't know Nevow, I just lurk on the discussions about it. I mention ZPT from time-to-time mainly out of selfishness: it would be easier for me to learn Nevow if it were more like ZPT ;)

Now, on to the reply...

mg's attr.tac has this in the template:

<ul nevow:data="links" nevow:render="sequence"> <li nevow:pattern="item" nevow:render="link"><a href="#" nevow:render="attribute href=link,alt=label"><nevow:slot name="label">label</nevow:slot></a></li> </ul>

I don't see what this does that is different to:

<ul tal:repeat="linkinfo context/links"> <li><a href="#" tal:attributes="href linkinfo/link; label linkinfo/label"/></li> </ul>

Although I don't totally understand why mg's attr.tac has a nevow:slot tag for label and not link, as far as I can tell the ZPT I give here is equivalent in concept. Explanations and/or corrections welcome!

Of course, my ZPT examples requires that the code would require there to be a linkinfo class, e.g.

class LinkInfo: def __init__(self, link, label): self.link = link self.label = label

And context/links would just be a list of these. I don't see this as being any more complex than what attr.tac does, though.

If nothing else, I hope this discussion can serve as the basis for a "Nevow for ZPT users" tutorial.

-Andrew.

On Wed, Oct 20, 2004 at 10:26:36AM +0100, Matt Goodall wrote:

On Tue, 2004-10-19 at 23:06 +0200, Andrew Bennetts wrote:

[...]

...

<ul tal:repeat="linkinfo context/links">
  <li><a href="#" tal:attributes="href linkinfo/link; label linkinfo/label"/></li>
</ul>

Although I don't totally understand why mg's attr.tac has a nevow:slot tag for label and not link, as far as I can tell the ZPT I give here is equivalent in concept. Explanations and/or corrections welcome!

The attribute renderer in attr.tac example updates updates from values in slots, i.e. href is set to the href slot and alt (yeah, it should be label;-)) is set to the label slot. The slot *inside* the <a>...</a> is actually nothing to do with the attribute renderer but ensures that the label also appears inside the element.

Oh, right. I get it now, duh :)

I don't know ZPT well enough to know if your example does exactly the same (I can't see how it could) but that really doesn't matter for this discussion anyway.

My ZPT to be equivalent should be:

<ul tal:repeat="linkinfo context/links"> <li><a href="#" tal:attributes="href linkinfo/link; alt linkinfo/label" tal:content="linkinfo/label"/>Label will go here</li> </ul>

I think it's a shame that no-one seems to know both ZPT and Nevow, as I suspect there may be something they can learn from each other, as they have some similar goals. I'd like to learn Nevow (although I'm really no ZPT expert), but time is always the problem...

I should point out that most of the time, I use the <n:attr ...

...

<n:slot ...></n:attr> syntax because it's always there and it's more

flexible. I wrote the attr.tac more as an example of how one might implement something like this using a renderer although it does have the benefit of being compact for really simple stuff.

...

Of course, my ZPT examples requires that the code would require there to be a linkinfo class, e.g.

class LinkInfo:
    def __init__(self, link, label):
        self.link = link
        self.label = label

And context/links would just be a list of these. I don't see this as being any more complex than what attr.tac does, though.

This is probably the right way with Nevow too. The difference with Nevow is that Nevow refuses to look inside objects it doesn't understand by default so it would never use getattr unless explicitly told to.

I don't know exactly where this happens in Zope 3, but it won't by default either. So, the code would look more like this:

from zope.interface import Interface, Attribute, implements

class ILinkInfo(Interface): link = Attribute('URI that a link points to') label = Attribute('Short description of the link')

class LinkInfo: implements(ILinkInfo) ...

And then usually in a ZCML file say that ZPT (or really the publisher in general) is allowed to access attributes and methods defined in ILinkInfo.

You can tell Nevow how to look inside objects by registering a inevow.IContainer adapter. We've talked about providing a IContainer adapter that does getattr magic in Nevow but it would be up to the developer to register the adapter for specific types.

I see. This seems essentially equivalent to the ZPT way -- registering an adapter from ILinkInfo to IContainer. Zope does things via security declarations because there's a desire to allow relatively untrusted sources to write page templates, I guess. There's more in common here than different, though :)

...

If nothing else, I hope this discussion can serve as the basis for a "Nevow for ZPT users" tutorial.

I guess I should learn ZPT properly sometime, just to get another angle on all this.

And I should learn Nevow :)

-Andrew.

On Oct 19, 2004, at 2:51 AM, Andrew Bennetts wrote:

TAL does allow this, in two ways (that I know of):

First, there's the hackish way:

<a tal:attributes="href python:'/users/' + context/username + 

'/images'" />

The second way is to put this sort of complex code a view:

class ViewBlah:
    def __init__(self, context, request):
        self.context = context
        self.request = request
    def imagesPath(self):
        return '/users/' + self.context.username + '/images'

then you can do:

<a tal:attributes="href view/imagesPath" />

Which is exactly what Nevow allows you to do very easily, as well. Currently, if you want to put this type of information in python code, you can use a technique similar to your second example:

def render_imagesPath(self, ctx, username): return ctx.tag(href=['/users/', username, '/images'])

If you'd rather put that information in the template, you can do it using nevow:attr:

<a><nevow:attr name="href">/users/<nevow:slot name="username" />/images</nevow:attr></a>

Again, the reason I arrived at this syntax is because it doesn't require you to learn any new substitution syntax and the full range of nevow functionality is available. It's consistent.

I don't see what the huge advantage of dreid's proposed nevow:attributes syntax is, in fact I'm not even sure how it would work. I'm against it mostly because it's another mechanism users have to learn, and is only useful for one small use case.

Another possibility is a python renderer:

<a nevow:render="python ctx.tag(href=["/users/", slot('username'), "/images"])" />

The implementation would be pretty simple:

def render_python(self, ctx, code): def evalIt(ctx, data): return eval(code, {'ctx': ctx, 'data': data}) return evalIt

dp