[Python-ideas] exclusively1, common, exclusively2 = set1 - set2, set1 & set2, set2 - set1

[Joshua Landau]

On 6 July 2013 05:56, Paddy3118 <paddy3118 at gmail.com> wrote:
> On Friday, 5 July 2013 22:38:22 UTC+1, Joshua Landau wrote:
>>
>> Hence why it should be defined:
>>
>>     set1.partition(set2) === set1 - set2, set1 & set 2
>>
>> That lets you have the "single pass" of each set as before, but is a
>> "smaller" operation. The full partition would just plot "set2 - set1"
>> on the end:
>>
>> ven_a, ven_shared = a.partition(b)
>> ven_b = ven_b - ven_shared
>>
>> And "ven_a | ven_shared == a" as you said.
>
> Unfortunately I tend to need all three of  exclusively1, common,
> exclusively2 . Assuming fast C implementations, then your proposal would
> lead to less opportunity for optimization and the need to create one needed
> result in Python. The need for all three and the potentially better
> optimization afforded to computing three at once in C should outweigh any
> considerations of the name of the method.

I don't believe it would be any (measurably) slower, given the
single-pass optimisations shown in other posts. I could be wrong, but
it's not like Python's known for it's micro-optimisations (except for
dicts...).

I also think that my way is better *because* of efficiency concerns --
if it's not measurably slower for the 3-way split, surely it's more
useful to allow people to have a fast 2-way split. It's also a
simpler, less redundant implementation.

I could give you some uses of my partition over 3-way partitioning:

flags = set(...)
flags_passed_to_next_in_chain, flags_kept = flags.partition(flags_that_I_want)

The rest are all variations of this.