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pcdshub / happi

Heuristic Access to Positions of Photon Instruments
https://pcdshub.github.io/happi/master
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Make `happi.SearchResult` hashable for usage in sets and such #255

Closed klauer closed 2 years ago

klauer commented 2 years ago

_Originally posted by @klauer in https://github.com/pcdshub/happi/pull/254#discussion_r888369082_

tangkong commented 2 years ago

A thought here: Typically you only want to hash immutable objects, lest their hashes change and they get lost in the hash table somewhere. The use case we are considering right now (finding intersections of sets of SearchResults) is innocuous enough, but a SearchResult is very much a mutable object.

Perhaps it shouldn't be though. If we're modifying a search result before instantiating an object or something similar, there's a problem

klauer commented 2 years ago

I think SearchResult isn't really intentionally mutable - just it has a dictionary of metadata that you could come along and modify if you so pleased.

Since each result pairs with a given identifier from the database, the hash key of a SearchResult could be something like (client, metadata["_id"])

tangkong commented 2 years ago

I have a working implementation that bases the hash on the metadata dictionary, which I was considering making a frozendict to alleviate my mutability concerns. I figure if we don't intend the object to be mutable we may as well force it to be as such.

For some reason I thought there was a frozendict in the standard library. I suppose we leave this be then