[Python-ideas] Revisiting Immutable Mappings

[Zaur Shibzukhov]

May be the following simple prototype of frozendict could be useful?

def frozen_error():
   return RuntimeError("frozendict is not mutable")

class frozendict(dict):
    #
    def __setitem__(self, key, val):
        raise frozen_error()
    #
    def setdefault(self, key, val=None):
        raise frozen_error()
    #
    def update(self, ob):
        raise frozen_error()
    #
    def pop(self):
        raise frozen_error()
    #
    def popitem(self, ob):
        raise frozen_error()
    #
    def clear(self, ob):
        raise frozen_error()
    #
    def __delitem__(self, key):
        raise frozen_error()
    #
    def __repr__(self):
        return "frozendict(" + dict.__repr__(self)[1:-1] + ")"
    #
    def __str__(self):
        return "frozendict(" + dict.__str__(self)[1:-1] + ")"
    #
    def fromkeys(self, keys, val=None):
        return frozendict([(key,val) for key in keys])
    #
    def copy(self):
        return frozendict(self.items())
        
среда, 10 октября 2018 г., 20:06:03 UTC+3 пользователь Philip Martin 
написал:
>
> 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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