Default value for nested dataclasses

May 5, 2023

I got the following dataclasses in Python:

@dataclass
class B(baseClass):

  d: float
  e: int


@dataclass
class A(baseClass):

  b: B
  c: str

I have this configured so that the baseClass allows to get the variables of each class from a config.json file. This file contains the following nested dictionary.

{
  a: {
    b: {
       "d": a_float_value
       "e": a_int_value
    }
    c: a_string_value
}

But the key "b" can be an empty dict.

{
  a: {
    b: {}
    c: a_string_value
}

But how do I integrate this into my dataclasses?
I tried

@dataclass
class B(baseClass):

  d: float
  e: int


@dataclass
class A(baseClass):

  b: Optional[B] = {}
  c: str

and

@dataclass
class B(baseClass):

  d: float
  e: int


@dataclass
class A(baseClass):

  b: B = field(default_factory=dict)
  c: str

But this doesn’t seem to work.

>Solution :

Could you try something like this by explicitly using the field class from dataclasses:

from typing import Dict, Optional
from dataclasses import dataclass, field

@dataclass
class B:

  d: float
  e: int

@dataclass
class A:
  c: str
  b: Optional[B] = field(default_factory=dict)


obj = A(c='sds')
print(obj.b)

Output was an empty dictionary for b variable.