how to convert a dict to a dataclass (reverse of asdict)?

Question

the dataclasses module lets users make a dict from a dataclass reall conveniently, like this:

from dataclasses import dataclass, asdict

@dataclass
class MyDataClass:
    ''' description of the dataclass '''
    a: int
    b: int
    
# create instance
c = MyDataClass(100, 200)
print(c)

# turn into a dict
d = asdict(c)
print(d)

But i am trying to do the reverse process: dict -> dataclass.

The best that i can do is unpack a dict back into the predefined dataclass.

# is there a way to convert this dict to a dataclass ?
my_dict = {'a': 100, 'b': 200}
e = MyDataClass(**my_dict)
print(e)

How can i achieve this without having to pre-define the dataclass (if it is possible) ?

Answer 1

You can use make_dataclass:

from dataclasses import make_dataclass

my_dict = {"a": 100, "b": 200}
make_dataclass(
    "MyDynamicallyCreatedDataclass", ((k, type(v)) for k, v in my_dict.items())
)(**my_dict)

Answer 2

I'd go with unpacking the dict as you showed.

from dataclasses import dataclass, asdict

@dataclass
class MyDataClass:
    a: int
    b: int

c = MyDataClass(100, 200)
print(c)
>>> MyDataClass(a=100, b=200)

d = asdict(c)
print(d)
>>> {'a': 100, 'b': 200}

e = MyDataClass(**d)
print(e)
>>> MyDataClass(a=100, b=200)

You can't turn a dictionary into a dataclass class that doesn't yet exist. You'll have to create the class before transforming a dict into it. If you really would rather have a class than a dictionary you could use an Enum. Otherwise you're just left with shortcut ways to make classes and then turning a dict into those classes.

Answer 3

You could use a SimpleNamespace Or a namedtuple. Although this would not be a dataclass it would be it's own object:

from types import SimpleNamespace
from collections import namedtuple

my_dict = {'a': 100, 'b': 200}

# SimpleNamespace solution
e = SimpleNamespace(**my_dict)

# namedtuple solution
MyClass = namedtuple("MyClass", my_dict)
f = MyClass(**my_dict)

---

>>> e
namespace(a=100, b=200)
>>> e.a
100
>>> 
>>> MyClass
<class '__main__.MyClass'>
>>> f
MyClass(a=100, b=200)
>>> f.a
100