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Sadly, the question with both this and ty is: Does it support pydantic? If not, then it's not really helpful for many people, and right now AFAIK neither suppor

Sadly, the question with both this and ty is: Does it support pydantic? If not, then it's not really helpful for many people, and right now AFAIK neither supports pydantic. Pydantic is probably the problem here, but it is what it is.

phailhaus 1y ago
Python's type system is the problem here, which cannot support even the native dataclass pattern and needs custom plugins written for each type checker.
- kstrauser 1y ago
  The type system’s alright. It just gets especially tricky when you’re trying to check code which won’t exist until you run it. For instance, suppose you wanted to load your own module from a database with something like foo = eval(result) It can’t know what you’re going to load until it actually does it. Things which lean heavily into metaprogramming, typically ORMs or things like Pydantic, fall into that category. I can’t hold that against the type system.
  - phailhaus 1y ago
    > I can’t hold that against the type system. I think we should. Dataclasses have existed in Python for an extremely long time, and yet the type system doesn't support defining your own similar classes. Kwargs have also existed forever, but they forgot to support that and had to add TypedDict's much later. And it still doesn't properly support optional fields. There's a lot of stuff like this in the language which are unbelievably frustrating, because for some reason they implemented the syntax before implementing a typechecker. Everything has been hacked in ever since. I consider python's type system to be a lost cause, just hoping for someone to make the Typescript equivalent for Python.
    - flanked-evergl 1y ago
      Dataclasses support optional fields and kwargs perfectly. Not sure what you are talking about. I don't think you understand what Pydantic brings to the table or why people use it. It has lots more to do with serialization, complex validation and data mapping.
      - phailhaus 1y ago
        kwargs are not dataclasses, they are dicts. TypedDict was shoehorned in later to allow typing dicts, but they are so poorly designed that you can't mark individual fields as optional.
  - bvrmn 1y ago
    I guess you didn't work with good type system then. Look for TS, for example. How it allows to make strong typing for pydantic-like libraries in FE world. All how it allows to type routers.
- flanked-evergl 1y ago
  I don't think this is really true, I think native data classes can do just about everything you need, it's just that you need some tooling around them to get the same as Pydantic offers. I'm pretty sure we are going to see better native dataclass support in Pydantic going forward. Already there is some support in Pydantic for native dataclasses: https://docs.pydantic.dev/latest/concepts/dataclasses/ https://docs.pydantic.dev/latest/concepts/dataclasses/
  - kitotik 1y ago
    I have used native dataclasses with pydantic starting with v1.5 and it’s only improved with the the newer 2.x releases. Aside from basic inheritance and complex nested types, the pydantic ‘TypeAdapter’ is awesome for simply validating native dataclasses. It’s a little slow, but everything pydantic is =)
  - phailhaus 1y ago
    There is no facility in the type system to express the idea that "whatever class attributes are defined, those are kwargs to the init function". That's hacked in using extra typechecker plugins. That's why we're sitting around talking about if a particular typechecker "supports pydantic", rather than it just working.
    - flanked-evergl 1y ago
      There is a way to indicate whatever class attributes are defined, those are kwargs to the init function. For one, you can use `kw_only` on the dataclass decorator [1], alternatively you can use the `kw_only` arg on the field function [2]. [1]: https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass https://docs.python.org/3/library/dataclasses.html#dataclass... [2]: https://docs.python.org/3/library/dataclasses.html#dataclasses.field https://docs.python.org/3/library/dataclasses.html#dataclass...
      - phailhaus 1y ago
        That's only for dataclasses, you can't implement your own class like this without implementing it as a dataclass, because the typechecking for it is hacked in as a custom plugin. What I'm trying to point out is that these features exist in core Python and yet the type system they built can't express it. By contrast, TypeScript is designed in such a way that you can implement everything yourself without having to write "custom typescript checker plugins".
ocamoss 1y ago
Pyrefly actually does have (experimental) support for Pydantic! https://pyrefly.org/en/docs/pydantic/ https://pyrefly.org/en/docs/pydantic/
- flanked-evergl 1y ago
  Nice, did not know.
mixmastamyk 1y ago
Why would they need to support pydantic when it uses standard annotations? I tried it with ty yesterday and it flagged issues as expected.
- flanked-evergl 1y ago
  Pydantic does some pretty strange stuff which works as expected but confuses the type checker unless you use the pydantic plugin. https://docs.pydantic.dev/latest/integrations/mypy/ https://docs.pydantic.dev/latest/integrations/mypy/
  - mixmastamyk 1y ago
    I see. Tried ty and it seemed to know about missing required args. But wasn't able to follow the Field directives.

phailhaus 1y ago

Python's type system is the problem here, which cannot support even the native dataclass pattern and needs custom plugins written for each type checker.

kstrauser 1y ago
The type system’s alright. It just gets especially tricky when you’re trying to check code which won’t exist until you run it. For instance, suppose you wanted to load your own module from a database with something like foo = eval(result) It can’t know what you’re going to load until it actually does it. Things which lean heavily into metaprogramming, typically ORMs or things like Pydantic, fall into that category. I can’t hold that against the type system.
- phailhaus 1y ago
  > I can’t hold that against the type system. I think we should. Dataclasses have existed in Python for an extremely long time, and yet the type system doesn't support defining your own similar classes. Kwargs have also existed forever, but they forgot to support that and had to add TypedDict's much later. And it still doesn't properly support optional fields. There's a lot of stuff like this in the language which are unbelievably frustrating, because for some reason they implemented the syntax before implementing a typechecker. Everything has been hacked in ever since. I consider python's type system to be a lost cause, just hoping for someone to make the Typescript equivalent for Python.
  - flanked-evergl 1y ago
    Dataclasses support optional fields and kwargs perfectly. Not sure what you are talking about. I don't think you understand what Pydantic brings to the table or why people use it. It has lots more to do with serialization, complex validation and data mapping.
    - phailhaus 1y ago
      kwargs are not dataclasses, they are dicts. TypedDict was shoehorned in later to allow typing dicts, but they are so poorly designed that you can't mark individual fields as optional.
- bvrmn 1y ago
  I guess you didn't work with good type system then. Look for TS, for example. How it allows to make strong typing for pydantic-like libraries in FE world. All how it allows to type routers.
flanked-evergl 1y ago
I don't think this is really true, I think native data classes can do just about everything you need, it's just that you need some tooling around them to get the same as Pydantic offers. I'm pretty sure we are going to see better native dataclass support in Pydantic going forward. Already there is some support in Pydantic for native dataclasses: https://docs.pydantic.dev/latest/concepts/dataclasses/ https://docs.pydantic.dev/latest/concepts/dataclasses/
- kitotik 1y ago
  I have used native dataclasses with pydantic starting with v1.5 and it’s only improved with the the newer 2.x releases. Aside from basic inheritance and complex nested types, the pydantic ‘TypeAdapter’ is awesome for simply validating native dataclasses. It’s a little slow, but everything pydantic is =)
- phailhaus 1y ago
  There is no facility in the type system to express the idea that "whatever class attributes are defined, those are kwargs to the init function". That's hacked in using extra typechecker plugins. That's why we're sitting around talking about if a particular typechecker "supports pydantic", rather than it just working.
  - flanked-evergl 1y ago
    There is a way to indicate whatever class attributes are defined, those are kwargs to the init function. For one, you can use `kw_only` on the dataclass decorator [1], alternatively you can use the `kw_only` arg on the field function [2]. [1]: https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass https://docs.python.org/3/library/dataclasses.html#dataclass... [2]: https://docs.python.org/3/library/dataclasses.html#dataclasses.field https://docs.python.org/3/library/dataclasses.html#dataclass...
    - phailhaus 1y ago
      That's only for dataclasses, you can't implement your own class like this without implementing it as a dataclass, because the typechecking for it is hacked in as a custom plugin. What I'm trying to point out is that these features exist in core Python and yet the type system they built can't express it. By contrast, TypeScript is designed in such a way that you can implement everything yourself without having to write "custom typescript checker plugins".

ocamoss 1y ago

Pyrefly actually does have (experimental) support for Pydantic! https://pyrefly.org/en/docs/pydantic/ https://pyrefly.org/en/docs/pydantic/

flanked-evergl 1y ago
Nice, did not know.

mixmastamyk 1y ago

Why would they need to support pydantic when it uses standard annotations? I tried it with ty yesterday and it flagged issues as expected.

flanked-evergl 1y ago
Pydantic does some pretty strange stuff which works as expected but confuses the type checker unless you use the pydantic plugin. https://docs.pydantic.dev/latest/integrations/mypy/ https://docs.pydantic.dev/latest/integrations/mypy/
- mixmastamyk 1y ago
  I see. Tried ty and it seemed to know about missing required args. But wasn't able to follow the Field directives.