What is the magic behind 'dataclass' decorator type-hint of dataclasses module?

I'm trying to deepen my understanding of how Python's dataclasses module works, particularly the role of type hints in defining class attributes.

When I define a dataclass like this:

from dataclasses import dataclass

@dataclass
class Person:
    name: str
    age: int

I notice that the type hints (str for name and int for age) are used by the dataclass decorator to generate various methods like __init__, __repr__, and __eq__ (I'm only interested in __init__). This automatic generation makes it very convenient, but I'm curious about the underlying mechanisms that enable this functionality.

Specifically, I have a question:

How does the dataclass decorator utilize type hints to generate these methods?

I’ve copied and pasted the same code from the original dataclasses file into my working directory with the name custom_dataclass (for testing purposes), but my linter did not recognize the __init__ attributes.

In picture1, you can see that when I try to instantiate the Person class, I correctly visualize all attributes mentioned in the Person class. This class uses the original @dataclass decorator. However, when I try the same with PersonCustom using the @custom_dataclass decorator, no attributes appear at all, as shown in picture2.

If anyone has any answers or insights, I’d like to hear them. Thanks in advance for your help!

I've also tried to see declarative_base method from sqlalchemy like

from sqlalchemy import Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class User(Base):
    __tablename__ = "user"

    id = Column(Integer, primary_key=True)
    name = Column(String)
    age = Column(Integer)


User()

but there no attributes appear either

[sqlalchemy] no attributes appear either

Well, there aren't any type hints involved. Rather we're assigning Column objects to those names, and each such object is storing a certain sql type (not a hint, not an annotation).

the type hints ... are used by the dataclass decorator

Yes. It accesses them via an API call. Details are in the documentation.

It appears your custom decorator is not making use of dataclass_transform() and is not doing work similar to what the @dataclass decorator does. Which is unsurprising, as there's a lot of work involved, at least when addressing the general case, about 1.5 KLOC of source code.