Do you have concern with speed or memory footprint of pydantic compared to the rest (attrs, dataclasses etc)? Pydantic seems insistent on parsing/validating the types at runtime (which makes good sense for something like FastAPI).
If you’re worried about the performance hit of extra crap happening at runtime… dear lord use another programming language.
Dataclasses is just… meh. Pydantic and Attrs just have so many great features, I would never use dataclasses unless someone had a gun to my head to only use the standard library. I don’t know of a single Python project that uses dataclasses where Pydantic or Attrs would do (I’m sure they exist, but I’ve never run across it).
Dataclasses honestly seems very reactionary by the Python devs, since Attrs was getting so popular and used everywhere that it got a little embarrassing for Python that something so obviously needed in the language just wasn’t there. Those that weren’t using Attrs runtime validators often did something similar to Attrs by abusing NamedTuple with type hints. There were tons of “why isnt Attrs in the stdlib” comments, which is an annoying type of comment to make, but it happens. So they added dataclasses, but having all the many features that Attrs has isn’t a very standard-library-like approach, so we got… dataclasses. Like “look, it’s what you wanted, right!?”. Well no not really, thanks we’ll just keep using Attrs and then Pydantic
Attrs just has the features I need for now. It certainly feel a touch verbose but I’m happy to pay the price.
id: UUID = attr.ib(validator=instance_of(UUID), …other parameters)
If your attribute name is longer or you have other parameters to set, that can be a very long line (or lines) of code that you repeat for every attribute
As I think I made clear in PEP 557, and every time I discuss this with anyone, dataclasses owes a lot to attrs. I think attrs made some great design decisions, in particular to metaclasses or base classes.
Python can be used quite successfully in high-performance environments if you are judicious about how you use it; set performance budgets, measure continuously, make sure to have vectorized interfaces, and have a tool on hand, like PyO3, Cython, or mypyc (you should probably NOT be using C these days, even if "rewrite in C" is the way this advice was phrased historically) ready to push very hot loops into something with higher performance when necessary. But if you redundantly validate everything's type on every invocation at runtime, it does eventually become untenable for anything but slow batch jobs if you have any significant volume of data.