Add a way to hide fields in dataclasses #89609

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1. formigacomcaimbra

   added

   3.11only security fixesonly security fixes

   type-featureA feature request or enhancementA feature request or enhancement

   on Oct 12, 2021
2. ericvsmith commented on Oct 12, 2021

   

   ericvsmith

   on Oct 12, 2021

   Member

   More actions

   Please explain what "hiding" does.
3. formigacomcaimbra commented on Oct 12, 2021

   

   formigacomcaimbramannequin

   on Oct 12, 2021

   MannequinAuthor

   More actions

   The objective of this feature is to add a way to omit fields of a dataclass when asdict or astuple is used.

   The main propuse is to add the hide parameter in field and add it as an attribute in the Field class.

   @dataclass
   class User:
       name: str
       ws: WebSocket = field(hide=True)
   
   
   user = User("NiumXp", None)
   assert asdict(user) == {"name": "NiumXp"}

   asdict will ignore all fields that have the hide attribute set as True.

   ---

   Actually a possible solution to do it is doing this:

   from dataclasses import *
   
   _asdict = asdict
   
   
   class WebSocket:
       pass
   
   
   def asdict(obj):
       def factory(it):
           fields = []
   
           for raw_field in it:
               name, _ = raw_field
   
               field = obj.__dataclass_fields__[name]
               if not field.metadata.get("hide"):
                   fields.append(raw_field)
   
           return dict(fields)
       return _asdict(obj, dict_factory=factory)
   
   
   @dataclass
   class User:
       name: str
       ws: WebSocket = field(metadata={"hide": True})
   
   
   user = User("NiumXp", None)
   assert asdict(user) == {"name": "NiumXp"}

   We need to make the same in astuple and to avoid writing field(metadata={"hide": True) multiple times we can use

   from functools import partial
   from dataclasses import field as _field
   
   field = _field(metadata={"hide": True})

   But, this means that we can't reuse the metadata parameter.

   👍React with 👍1Reacted by cschroeer
4. ericvsmith commented on Oct 13, 2021

   

   ericvsmith

   on Oct 13, 2021

   Member

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   "hide" is not a good name for this.

   Does attrs have anything equivalent? This seems like a pretty niche usage, so I'm not inclined to include it without evidence of a wide-spread need for it.
5. ericvsmith

   self-assigned this

   on Oct 13, 2021
6. ezio-melotti

   transferred this issue fromon Apr 10, 2022
7. iritkatriel

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Nov 27, 2023