[PEAK] How do I extract a subset?

[Phillip J. Eby]

At 09:23 AM 4/17/2008 +0300, Peter Damoc wrote:
>     @trellis.observer
>     def updateView(self):
>         x = len(self.records) # needed to monitor changes
>         self.filtered_records = [x for x in self.records]

You can't modify trellis data in an observer.  Move this line to a 
rule of its own, and change it to:

     @trellis.rule
     def do_filtering(self):
         self.filtered_records.clear()
         self.filtered_records.update(x for x in self.records if x...)

This way, the same set object will be updated in-place.  Your 
observer should now check 'self.sorted_records.changes' instead of 
'len(self.records)' to ensure it's triggered when a change occurs.

Meanwhile, the reason that you're getting a conflict is because you 
are assigning different values to the filtered_records attribute in 
two places during the same calculation.