[PEAK] Computed sets

[Sergey Schetinin]

Also, if FilteredSubset.condition creates extra dependencies, when
those change it will recalculate .added, but it that dependency makes
some items to change their filtered state it will not be reflected in
.added / .removed

On Sat, Mar 14, 2009 at 07:56, Sergey Schetinin <maluke at gmail.com> wrote:
> It seems that the case when the same item is added to one source set
> of a UnionSet and removed from another, isn't handled: that item would
> appear on both .added and .removed.
>
> If it were only for .added and .removed attributes I'd go for a
> @maintain(make=Set)
> def set3(self):
>    s = self.set3
>    s.clear()
>    s.update(self.set1)
>    s.update(self.set2)
>    return s
>
>
>
>
> On Sat, Mar 14, 2009 at 04:22, Adam Atlas <adam at atlas.st> wrote:
>> I'm writing a module based on Trellis which provides several Set-like
>> objects, which can generally be used like Set or FrozenSet (plus the Trellis
>> .added and .removed attributes) but are generated dynamically from some
>> source sets, either by filtering one source set or by applying some standard
>> set operation (union, intersect, difference, symmetric difference) to two
>> source sets. The idea is to do this more efficiently by watching for changes
>> in the source sets and changing the computed set appropriately, rather than
>> having, say, a trellis.compute(lambda self: self.set1.union(self.set2)),
>> which would require the whole set to be rebuilt any time set1 or set2 change
>> at all, and also wouldn't expose the .added and .removed attributes.
>>
>> So here's how I'm doing it right now. Before I go further I just thought I'd
>> post it here to see if I'm on the right track, or if there's anything wrong
>> with this general approach.
>>
>>
>> class FilteredSubset(sets.BaseSet, trellis.Component):
>>    source = trellis.make(trellis.Set, writable=True)
>>    condition = trellis.attr(lambda self, val: True)
>>    _data = trellis.Set._data
>>
>>    def __init__(self, source=None, condition=None, **kw):
>>        trellis.Component.__init__(self, **kw)
>>        if condition is not None:
>>            self.condition = condition
>>        if source is not None:
>>            self.source = source
>>            self._data.update((k, True) for k in source._data if
>> self.condition(k))
>>
>>    @trellis.compute
>>    def added(self):
>>        return set(k for k in self.source.added if self.condition(k))
>>
>>    @trellis.compute
>>    def removed(self):
>>        return set(k for k in self.source.removed if k in self)
>>
>>
>>
>> class UnionSet(sets.BaseSet, trellis.Component):
>>    source1 = trellis.make(trellis.Set, writable=True)
>>    source2 = trellis.make(trellis.Set, writable=True)
>>    _data = trellis.Set._data
>>
>>    def __init__(self, source1=None, source2=None, **kw):
>>        trellis.Component.__init__(self, **kw)
>>        if source1 is not None:
>>            self.source1 = source1
>>            self._data.update(dict.fromkeys(source1, True))
>>        if source2 is not None:
>>            self.source2 = source2
>>            self._data.update(dict.fromkeys(source2, True))
>>
>>    @trellis.compute
>>    def added(self):
>>        '''
>>        something is added to UnionSet if it is added to at least one source
>>        set and it was not already in either source set
>>        '''
>>        return self.source1.added.difference(self.source2).union(
>>            self.source2.added.difference(self.source1))
>>
>>    @trellis.compute
>>    def removed(self):
>>        '''
>>        something is removed from UnionSet if it is removed from both source
>>        sets, or if it is removed from one source set and it is not in the
>>        other source set
>>        '''
>>        return self.source1.removed.difference(self.source2).union(
>>            self.source2.removed.difference(self.source1))
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>>
>
>
>
> --
> Best Regards,
> Sergey Schetinin
>
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> http://word-to-html.com/ -- Word to HTML Converter
>



-- 
Best Regards,
Sergey Schetinin

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