[Python-ideas] Revisiting Immutable Mappings

[Anders Hovmöller]

In tri.struct we have a class Frozen https://github.com/TriOptima/tri.struct/blob/master/lib/tri/struct/__init__.py that can be used to freeze stuff. I think something like this would be even better in the standard library, especially now with data classes! If we had this frozendict would just be:

class frozendict(dict, Frozen):
    pass

/ Anders

> On 10 Oct 2018, at 19:04, Philip Martin <philip.martin2007 at gmail.com> wrote:
> 
> Hi, I first want to thank everyone in the community for the contributions over the years. I know the idea of a frozendict has been proposed before and rejected. I have a use case for a frozendict implementation that to my knowledge was not discussed during previous debates. My reasoning for a frozendict class stems from patterns I typically see arise when performing ETL or data integrations and conversions. I generally have used MappingProxyType as a way to set default mapping to a function or to set an empty mapping to a function. I've created a gist with an example use case:
> 
> https://gist.github.com/pmart123/493edf84d9aa61691ca7321325ebb6ab
> 
> I've included an example of what code typically looks like when using MappingProxyType and what it could look like with a frozendict implementation. I believe this use case may also be under-reported in open source code as it often crops up when integrating third-party data sources, which at times can't be open sourced due to licensing issues. I would love to hear if anyone has used MappingProxyType in a similar manner, or if this use case could help warrant a frozendict in the standard library.
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