Check if the data can be structured without actually structuring it

• cattrs version: 22.2.0
• Python version: 3.10
• Operating System: Windows 10

Description

I have a dataclass that can be instantiated (structured) with a from_dict method, in this way I know all the typings are correct:

from dataclasses import Field, asdict, dataclass, fields
from cattrs import Converter

@dataclass
class MyDataClass:
    a: str
    b: int

    def validate_types(self) -> None:
        self.from_dict(asdict(self))

    @classmethod
    def from_dict(cls, data: dict, converter: Converter = get_converter()):
        return converter.structure(data, cls)

It also has a validate_types method that can be run after instantiation

What I Did

I would like to add the validate_types in the post_init:

from dataclasses import Field, asdict, dataclass, fields
from cattrs import Converter

@dataclass
class MyDataClass:
    a: str
    b: int

    def __post_init__(self):
        self.validate_types()

    def validate_types(self) -> None:
        self.from_dict(asdict(self))

    @classmethod
    def from_dict(cls, data: dict, converter: Converter = get_converter()):
        return converter.structure(data, cls)

unfortunately this ends in an infinite loop, because the from_dict generates a new instance of the class and the code goes into the post_init which calls validate_types, which calls from_dict, which creates a new instance of the class which goes into the post_init and on and on.

would it be possible for you to expose a function/method of the converter that only checks if the data can be structured without actually structuring/creating the new instance?

Start with Converter.structure and the example's from_dict and post_init flow to understand where recursive instance creation occurs. Define what a non-structuring validation operation should guarantee, then verify the behavior against the dataclass example and its recursive case.