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

[Paddy3118]

I found myself repeating something that I know I have used before, several 
times: I get two sets of results, may be sets of the passing tests when a 
design has changed, and I need to work out what has changed so work out 

1. What passed first time round
2. What passed both times.
3. What passed only the second time round.

I usually use something like the set equations in the title to do this but 
I recognise that this requires both sets to be traversed at least three 
times which seems wasteful.

I wondered if their was am algorithm to partition the two sets of data into 
three as above, but cutting down on the number of set traversals?

I also wondered that if such an algorithm existed, would it be useful 
enough to be worth incorporating into the Python library? 

Maybe defined as:

exclusively1, common, exclusively2 = set1.partition(set2)

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