Hi Larry, sets (and mappings, ie dicts), have a common functionality among many languages and libraries that does Not include an ordering. Already, in CPython, there is a need to somehow indicate that insertion ordering is being used in dicts or use OrderedDict. I am quite happy with keeping sets as they are and coding any extra functionality required on top of this. This aids me as I work in many languages that have their own sets and mappings, usually without any insertion ordering.
Cheers, Paddy. On Sun, Dec 29, 2019, 12:07 AM Larry Hastings <la...@hastings.org> wrote: > > On 12/27/19 7:44 PM, Tim Peters wrote: > > [Nick Coghlan <ncogh...@gmail.com> <ncogh...@gmail.com>] > > I took Larry's request a slightly different way: he has a use case where > he wants order preservation (so built in sets aren't good), but combined > with low cost duplicate identification and elimination and removal of > arbitrary elements (so lists and collections.deque aren't good). Organising > a work queue that way seems common enough ... > > > Is it? I confess I haven't thought of a plausible use case. Larry > didn't really explain his problem, just suggested that an ordered set > would be "a solution" to it. > > > Here is the original description of my problem, from the original email in > this thread. I considered this an adequate explanation of my problem at > the time. > > > On 12/15/19 6:48 PM, Larry Hastings wrote: > > I do have a use case for this. In one project I maintain a "ready" list of > jobs; I need to iterate over it, but I also want fast lookup because I > soemtimes remove jobs when they're subsequently marked "not ready". The > existing set object would work fine here, except that it doesn't maintain > insertion order. That means multiple runs of the program with the same > inputs may result in running jobs in different orders, and this instability > makes debugging more difficult. I've therefore switched from a set to a > dict with all keys mapped to None, which provides all the set-like > functionality I need. > > > In subsequent emails I've clarified that my workloads are small > enough--and computers are fast enough--that almost any data structure would > work fine for me here, e.g. a list. I don't think my needs should drive > the decision making process regardless. I only described my problem to get > the conversation rolling. > > I opine that anybody who iterates over set objects and has bugs in their > code would appreciate set objects maintaining insertion order. I suspect > it would make their debugging easier, because given identical inputs their > set iteration would behave identically, thus making their bugs that much > more stable. That's as much use case as I have for the feature. > > > */arry* > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/XWTP7OD4UMGL7DLVABM3S2CB26LN5RBP/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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