Message337864
I apologize - I should have been clearer about what this accomplishes. I'll use list addition as an example, but this works for any binary operation on these containers.
If the left operand has a refcount of exactly one, it will simply mutate in-place rather than making an unnecessary copy. The simplest example of this is with literals:
[0] + list1
This just modifies the literal [0] in-place rather than creating an unnecessary copy. However, the more common use case is adding named lists. Currently, when adding list1 + list2 + list3, two copies (with one reference each) are made:
- The intermediate result of list1 + list2.
- The sum of this intermediate result and list3.
Only the second of these is actually returned - the first is used once and thrown away. The effect of this patch is to only create *at most one* (instead of n-1) copy for any arbitrarily long list summation, as this intermediate result will just mutate in-place for lists 3-n. |
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Date |
User |
Action |
Args |
2019-03-13 16:57:42 | brandtbucher | set | recipients:
+ brandtbucher, tim.peters, arigo, rhettinger, serhiy.storchaka, pablogsal |
2019-03-13 16:57:42 | brandtbucher | set | messageid: <1552496262.14.0.420788786889.issue36229@roundup.psfhosted.org> |
2019-03-13 16:57:42 | brandtbucher | link | issue36229 messages |
2019-03-13 16:57:42 | brandtbucher | create | |
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