Previous discussions on this:
https://mail.python.org/archives/list/python-ideas@python.org/thread/ASHOHN32BQPBVPIGBZQRS24XHXFMB6XZ/
https://mail.python.org/archives/list/python-ideas@python.org/thread/K5SS62AB5DFFZIJ7ASKPLB2P3XGSYFPC/
(seems
like part of the above discussion that got separated)
https://mail.python.org/archives/list/python-ideas@python.org/thread/CKF2GFI3HKQAAYRCMMRPTFMONG3UGO4T/#CKF2GFI3HKQAAYRCMMRPTFMONG3UGO4T
On Thu, Jun 25, 2020 at 4:30 PM Ben Avrahami <avrahami....@gmail.com> wrote:
> Hey all,
> Often I've found this kind of code:
>
> seen = set()
> for i in iterable:
> if i in seen:
> ... # do something in case of duplicates
> else:
> seen.add(i)
> ... # do something in case of first visit
>
> This kind of code appears whenever one needs to check for duplicates in
> case of a user-submitted iterable, or when we loop over a recursive
> iteration that may involve cycles (graph search or the like). This code
> could be improved if one could ensure an item is in the set, and get
> whether it was there before in one operation. This may seem overly
> specific, but dicts do do this:
>
> seen = {}
> for i in iterable:
> if seen.set_default(i, some_value) is not None:
> ... # do something in case of duplicates
> else:
> ... # do something in case of first visit
>
> I think the set type would benefit greatly from its add method having a
> return value. set.add would return True if the item was already in the set
> prior to insertion, and False otherwise.
>
> Looking at the Cpython code, the set_add_entry already detects existing
> entries, adding a return value would require no additional complexity.
>
> Any thoughts?
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