unpack dataclasses/types or subsets of them to act as typed dict

Feature

often times helper methods take all the fields or subsets of the fields of a type/dataclass

in coordination with #4441

@dataclass
class MyModel:
   id: uuid
   name: str
   hostname: str
   memory_size: int

and i want to declare helpers like

# bad names
Magic = SubsetTypedDict(MyModel, exclude=["id"], total=False)

def wait_for_update(model_or_id: Model|uuid, **kw: Magic) -> Model:
   ...

** context **

spin out of #4441, based on my comment and the suggestion in

There's already a PR to make this happen: #8583

@AlexWaygood

@AlexWaygood i strongly disagree

my understanding is that the pr makes mypy pretends that the return value of the as_dict methods is a matching typed dict
it does not in any way give access to that type for other usage in the actual code

I see, apologies. Your proposed new way of constructing a TypedDict (a SubsetTypedDict), however, looks like it would probably require a PEP. It should probably be discussed over at the https://github.com/python/typing issue tracker rather than here, since it would impact the typing ecosystem as a whole rather than mypy.

I'm closing, because I don't think this is the appropriate forum for this kind of feature request, but please feel free to open a new issue at https://github.com/python/typing or to start a discussion on the typing-sig mailing list.

@RonnyPfannschmidt

@RonnyPfannschmidt I propose as a next step, writing this out on the typing-sig list and seeing what the reception is

I think the conversation it'd generate (whether there's overlap with someone else or a PEP) would be fruitful. Would you like to write a message there?

Unfortunately my bandwidth for this is currently zero, and likely to stay like that for the next few months

@RonnyPfannschmidt

@RonnyPfannschmidt No problem. Is it okay if in the future if someone stumbles upon this they can cite this as an idea on the typing-sig list if they want to?

Yes

@RonnyPfannschmidt

Hi @RonnyPfannschmidt curious if you know if this was ever formally proposed/superseded by something else? Very interested in this functionality

Nope still missing as fas as i know

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unpack dataclasses/types or subsets of them to act as typed dict #12906

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unpack dataclasses/types or subsets of them to act as typed dict #12906

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AlexWaygood commented on May 30, 2022

RonnyPfannschmidt commented on May 30, 2022

AlexWaygood commented on May 30, 2022

AlexWaygood commented on May 31, 2022

tony commented on Jul 11, 2022

RonnyPfannschmidt commented on Jul 11, 2022

tony commented on Jul 12, 2022

RonnyPfannschmidt commented on Jul 13, 2022

kdkavanagh commented on Oct 6, 2025

RonnyPfannschmidt commented on Oct 6, 2025

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