Message275707
Proposal from SO: in the iteration loop for 'myset.difference(iterable)', add equivalent of "if not myset: break'.
https://stackoverflow.com/questions/39378043/why-does-pythons-set-difference-method-take-time-with-an-empty-set
In the toy example for testing that this is currently not so, myset starts empty, but it was noted by the OP that a more realistic example would be that myset becomes empty after deletions.
Postulated reasons why not to do this (as opposed to why it has not been done yet ;-):
1) averaged over all uses, the time saved not iterating would be less than the time spent testing emptyness.
2) an implicit guarantee to complete the iteration for possible side-effects.
One answer notes that myset.difference(anotherset) is special-cased and faster than the equivalent non-set iterable.
I searched the tracker for 'empty set difference' and got no hits. If I remember, I will post any disposition of this issue back to SO. |
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Date |
User |
Action |
Args |
2016-09-10 22:22:04 | terry.reedy | set | recipients:
+ terry.reedy, rhettinger |
2016-09-10 22:22:04 | terry.reedy | set | messageid: <1473546124.61.0.846799872363.issue28071@psf.upfronthosting.co.za> |
2016-09-10 22:22:04 | terry.reedy | link | issue28071 messages |
2016-09-10 22:22:04 | terry.reedy | create | |
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