On 12/27/19 7:44 PM, Tim Peters wrote:
[Nick Coghlan <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/
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