Can you do wrapping generic types properly without a mypy plugin?#1500

cjw296 started this conversation inGeneral

cjw296

Oct 30, 2023

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cjw296
Oct 30, 2023

I think it's a relatively common pattern to have some kind of object that represents a value at a later date, or some other kind of "wrapping" type, such as a TwistedDeferred, asyncio or concurrentFuture, etc. But how do we get type checking of the results of getting attributes of these?

Concretely:

https://github.com/cjw296/generative_typing/blob/main/bag.py

...which can be used like:

@dataclassclassMyDataClass:foo:intbar:strbag_dataclass:Bag[MyDataClass]=Bag[MyDataClass](MyDataClass(foo=1,bar='x'))# Happy path examplesbag_dataclass_foo:Bag[int]=bag_dataclass.foofoo:int=bag_dataclass.foo.get()foo_:int=bag_dataclass_foo.get()bag_dataclass_bar:Bag[str]=bag_dataclass.barbar:str=bag_dataclass.bar.get()bar_:str=bag_dataclass_bar.get()classMyTypedDict(TypedDict):foo:intbar:strbag_typeddict:Bag[MyTypedDict]=Bag[MyTypedDict]({'foo':1,'bar':'x'})# Happy path examplesbag_typeddict_foo:Bag[int]=bag_typeddict.foodfoo:int=bag_typeddict.foo.get()dfoo_:int=bag_typeddict_foo.get()bag_typeddict_bar:Bag[str]=bag_typeddict.bardbar:str=bag_typeddict.bar.get()dbar_:str=bag_typeddict_bar.get()

I've got thisworkingwith amypy plugin, but how could I get this to work so that pylance, ruff, etc would also work?

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sobolevn
Oct 30, 2023

Nope,__getattr__ support without a plugin is not possible at the moment.
However, this pattern is quite common.

Maybe it is time to start a discussion about potentialProxy type? Likedef __getattr__(self, val: str) -> Proxy[MyDataClass]: and thenreveal_type(bag_typeddict.bar) would reveal"builtins.str".

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