On 18 juin, 00:14, Eric <[EMAIL PROTECTED]> wrote:
> This isn't a bug but it's something that might need to be documented
> to prevent folks from doing something that may hurt them later:
>
(snip)
>
> repr_node = ReprNode("obj")
>
> for i in range(10):
> repr_node.render(context)
>
> Can you tell what the problem? We're calling the render method
> on the same instance of the Node.
>
> Let's peek under the covers and look at ReprNode's definition::
>
> class ReprNode(template.Node):
> def __init__(self, obj)
> self.obj = obj
>
> def render(self, context):
> self.obj = template.resolve_variable(self.obj, context)
> return str(self.obj)
>
> def do_repr(parser, token):
> tag_name, obj = token.split_contents()
> return ReprNode(obj)
>
> Now look at what's going on. self.obj is assumed to be the name of
> the
> variable in the context. That's fine when render is called once.
> When render
> called a second time, self.obj is now the actual value of obj from the
> context.
This is exactly what you asked for. The cure is obvious : *don't*
rebind self.obj in render().
>
> I made the assumption that render() is only called once.
Wrong assumption. The mere fact that the context is passed to the
render method and not to the initialiser should be a good enough
indication that the same node instance can be rendered many times with
different contexts. If this wasn't the case, you wouldn't need a Node
class - a plain function would be enough.
> You don't
> realize that inside a for tag, the render method is called
> repeatedly.
It would be very unoptimal to reparse the for block content,
reinstanciate new Nodes and call their render method on every
iteration.
> This can cause tons of issues. If it wasn't a huge
> design change, TemplateTag should probably be Static classes.
What's a "Static" class ???
> I don't know if this is technically a bug in the Django templating
> system,
It isn't, obviously.
> bad design,
Neither.
> bad documentation,
I wouldn't call it "bad". Now everything can be improved, and since
explicit is better than implicit, it might be worth adding a note
explaining that point.
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