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 --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
