How to validate typing attributes in Python 3.7

Question

I want to validate since the instance creation if the type is right or wrong, i tried using @dataclass decorator but doesn't allow me to use the __init__ method, i also tried using a custom like class type

also in order of the type made some validations (if is a int, that field>0 or if is a str clean whitespaces, for example), i could use a dict to validate the type, but i want to know if there's a way to do it in pythonic way

class Car(object):
    """ My class with many fields """

    color: str
    name: str
    wheels: int

    def __init__(self):
        """ Get the type of fields and validate """
        pass

Answer 1

You can use the __post_init__ method of dataclasses to do your validations.

Below I just confirm that everything is an instance of the indicated type

from dataclasses import dataclass, fields

def validate(instance):
    for field in fields(instance):
        attr = getattr(instance, field.name)
        if not isinstance(attr, field.type):
            msg = "Field {0.name} is of type {1}, should be {0.type}".format(field, type(attr))
            raise ValueError(msg)

@dataclass
class Car:
    color:  str
    name:   str
    wheels: int    
    def __post_init__(self):
        validate(self)