Well, I think my suggestion is obviously that when a template tag is
in a loop, it should be re-initiated on every iteration, since that
would avoid unexpected and non-obvious side effects.
-Scott
On May 5, 2:52 pm, "burc...@gmail.com" <burc...@gmail.com> wrote:
> Hi Apreche,
>
> I don't want to be rude, but you probably wanted to send this to
> django-users, it is the place full of users of django framework who
> should be aware of your problem and this point of confusion (hm, or
> should it be blog post so everyone can google on their problem and
> find your message?).
> Everyone here in django-dev assumes that you have suggestion to fix
> something in django if you're writing here.
> Probably, you might suggest to improve django documentation where it
> explains how to create custom template tags.
> It seems you're really good at writing documentation!
> Then, please, go on, improve the current documentation text, create a
> ticket, and send your patch.
>
>
>
> On Wed, May 5, 2010 at 10:12 PM, Apreche <apre...@gmail.com> wrote:
> > I had a really strange bug in one of my custom template tags today. It
> > took me the entire morning to figure it out, but I finally did. I'm
> > not sure if it's a bug or a feature, but I wanted to make a post to
> > help the next person who has this same problem.
>
> > Let's pretend you make a custom template tag foo. The render method
> > for foo is in a class FooNode, and you pass it a person from the
> > context.
>
> > {% foo persona %}
> > {% foo personb %}
>
> > Then, as is common, you have a list of people that you render with a
> > loop in the template.
>
> > {% for person in people %}
> > {% foo person %}
> > {% endfor %}
>
> > It turns out that when a template tag stands alone, the __init__ of
> > FooNode will be called each time the template tag appears. However,
> > when the template tag is inside of a loop, the __init__ of the FooNode
> > is only called once. That single instance of FooNode sticks around,
> > and it's render method is called over and over as the loop goes
> > around.
>
> > This doesn't seem like that big of a deal. However, my template tag
> > was written in such a way that data members of FooNode were being set
> > in the __init__ and reused in the render(). Because the initialization
> > only happened the first time through the loop, the template tag always
> > rendered as if it was for the first person in the list. Those data
> > members carried over to subsequent renders because the Node was not
> > reinitialized. I managed to fix it, but be aware. If your template
> > tags are behaving strangely when they are in loops, this is probably
> > the issue.
>
> --
> Best regards, Yuri V. Baburov, ICQ# 99934676, Skype: yuri.baburov,
> MSN: bu...@live.com
>
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