Python dataclass from a nested dict

Question

The standard library in 3.7 can recursively convert a dataclass into a dict (example from the docs):

from dataclasses import dataclass, asdict
from typing im         


        

Answer 1

Using no additional modules, you can make use of the __post_init__ function to automatically convert the dict values to the correct type. This function is called after __init__.

from dataclasses import dataclass, asdict


@dataclass
class Bar:
    fee: str
    far: str

@dataclass
class Foo:
    bar: Bar

    def __post_init__(self):
        if isinstance(self.bar, dict):
            self.bar = Bar(**self.bar)

foo = Foo(bar=Bar(fee="La", far="So"))

d= asdict(foo)
print(d)  # {'bar': {'fee': 'La', 'far': 'So'}}
o = Foo(**d)
print(o)  # Foo(bar=Bar(fee='La', far='So'))

This solution has the added benefit of being able to use non-dataclass objects. As long as its str function can be converted back, it's fair game. For example, it can be used to keep str fields as IP4Address internally.