Re: Computed sets

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 <[email protected]> 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 <[email protected]> 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))
>>
>>    -mAtNS9Uf36hla/[email protected]
>>    def added(self):
>>        return set(k for k in self.source.added if self.condition(k))
>>
>>    -mAtNS9Uf36hla/[email protected]
>>    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))
>>
>>    -mAtNS9Uf36hla/[email protected]
>>    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))
>>
>>    -mAtNS9Uf36hla/[email protected]
>>    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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>



-- 
Best Regards,
Sergey Schetinin

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