[Python-ideas] Implement __add__ for set and frozenset

[Arnaud Delobelle]

2008/6/3 Arnaud Delobelle <arnodel at googlemail.com>:
>
> On 3 Jun 2008, at 02:21, George Sakkis wrote:
>
>> Regardless of the operator, that's a pretty inefficient way of doing
>> "unionall"; it creates N-1 intermediate result sets that discards them right
>> after they are added. It should be written as:
>>
>> big_u = set()
>> for s in all_sets:
>>    big_u.update(s)
>>
>> I wouldn't mind having a standard unionall, but not every 3-line function
>> has to be in the stdlib.
>>
>> George
>>
>
>
> Perhaps it would be nice to have set.union (and set.intersection) to accept
> more than one argument, i.e. have
>
>    A = S.union(T, U, V)
>
> mean
>
>    A = S.union(T)
>    A.update(U)
>    A.update(V)
>
> As a consequence of Python method implementation, one could write instead:
>
>    A = set.union(S, T, U, V)
>    B = set.intersection(S, T, U, V)
>
> which reads nicely

I've written a patch [1] that does that.  Following the suggestion of
Raymond Hettinger, I've implemented set.intersection by sorting all
its sets/frozensets/dicts in increasing order of size first, then
iterating over the smallest.  It's the first time I try my hand at
this so it might not be up to much, but I've made it so I might as
well send it :).  It's against py3k svn.

[1] http://bugs.python.org/issue3069

-- 
Arnaud