I may be the only one still interested in this, but the patch got incorporated yesterday (http://code.djangoproject.com/changeset/6981), so Malcolm, your original idea will now work.
--Ned. Ned Batchelder wrote: > I tried out this change, and it works well. I've created a ticket > (http://code.djangoproject.com/ticket/6295) with a patch. > > --Ned. > http://nedbatchelder.com > > Ned Batchelder wrote: >> Malcolm, thanks for continuing this (I was away for a few days). I >> was thinking about the forloop internals as well, and it seems to me >> that there's no reason the forloop dictionary needs to be completely >> new each time around. Why not change forloop to create a new >> dictionary before the first iteration, then update the dictionary on >> each iteration rather than replace it? >> >> BTW: this problem also plagues ifchanged: the docs say "check if a >> value has changed from the last iteration of a loop", which I guess >> is accurate, but I was surprised to find that it really only works if >> the ifchanged tag is evaluated on every iteration of the loop. >> >> --Ned. >> >> Malcolm Tredinnick wrote: >>> Hey Ned, >>> >>> On Sat, 2007-12-29 at 08:27 +1100, Malcolm Tredinnick wrote: >>> [...] >>> >>>> def render(self, context): >>>> if context[self.varname] == id(context['forloop']): >>>> return self.nodelist_false.render(context) >>>> context[self.varname] = id(context['forloop']) >>>> return self.nodelist_true.render(context) >>>> >>> >>> This guess is rubbish. The problem is that the context['forloop'] >>> dictionary is a new instance for every iteration of the for-loop, so >>> there's nothing constant about that outer structure we can use. >>> >>> After a bit of sleep, some food and some time spent thinking about this >>> whilst doing other stuff today, there's a better solution (a.k.a one >>> that works) attached to this mail. I've even tested this one. >>> >>> During any for-loop, the only thing that remains constant is the >>> "parentloop" dictionary. That dictionary is created anew every time the >>> *parent* loop steps forwards, but it is referred to by reference for >>> each iteration of the inner loop. So we can stick a marker into the >>> parent loop's data structure (even when there's no parent loop, that >>> data structure is an empty dictionary). >>> >>> So, this implementation does depend a bit on the internals of the >>> ForNode, but that isn't a complete crime. Plus it's been hard to come up >>> with an alternative. Every time I thought of some tricky data structure >>> that seemed to do the trick, I was able to break it. A template fragment >>> such as >>> >>> {% for x in data %} >>> {% if x %} >>> {% iffirst %} yes {% else %} no {% endfirst %} >>> {% else %} fail {% endif %} >>> {% endfor %} >>> >>> given data = (0, 1, 1, 0) twice in succession (without recompiling), or >>> giving data = (0, 1, 1, 0) and data = (0, 0, 1, 0) on successive runs >>> (again, without recompiling) was enough to break most of my attempts. >>> >>> It's also not too hard to extend this to be check whether this is the >>> first time around the parent loop using a similar method, although >>> nested "iffirst" tags seems hard. >>> >>> Best wishes, >>> Malcolm >>> >>> >> >> -- >> Ned Batchelder, http://nedbatchelder.com >> >> >> > > -- > Ned Batchelder, http://nedbatchelder.com > > > > -- Ned Batchelder, http://nedbatchelder.com --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
