[Python-ideas] Make types.MappingProxyType hashable

Emanuel Barry vgr255 at live.ca
Thu Jul 28 18:23:35 EDT 2016

> From: Guido van Rossum
> Sent: Thursday, July 28, 2016 6:06 PM
> To: Emanuel Barry
> Cc: python-ideas at python.org
> Subject: Re: [Python-ideas] Make types.MappingProxyType hashable
> I think you misunderstand the distinction between immutable and
> read-only. MappingProxyType is read-only -- you cannot modify the
> underlying dict through the proxy. But it's not immutable -- if the
> underlying dict is changed directly (e.g. by assignment to a class
> attribute) the proxy is changed too. So making the proxy hashable
> would be a mistake.

Oh, I didn't know that this was just a view over an actual dict. I guess that solves the question :)

> What real-world use case do you have for this?

Not me, actually. Someone in #python asked about an immutable dict, and I pointed them towards mappingproxy, only to realize it wasn't hashable. Maybe something like frozendict could be added, though? At this point I don't really have an opinion, so it's up to the list to decide if they want it or not :)


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