Make the Python json encoder support Python's new dataclasses

Question

Starting with Python 3.7, there is something called a dataclass:

from dataclasses import dataclass

@dataclass
class Foo:
    x: str

However, t

Answer 1

Ways of getting JSONified dataclass instance

There are couple of options to accomplish that goal, selection of each imply analyze on which approach suits best for your needs:

Standart library: dataclass.asdict

import dataclasses
import json


@dataclass.dataclass
class Foo:
    x: str

foo = Foo(x='1')
json_foo = json.dumps(dataclasses.asdict(foo)) # '{"x": "1"}'

Picking it back to dataclass instance isn't trivial, so you may want to visit that answer https://stackoverflow.com/a/53498623/2067976

Marshmallow Dataclass

from dataclasses import field
from marshmallow_dataclass import dataclass


@dataclass
class Foo:
    x: int = field(metadata={"required": True})

foo = Foo(x='1') # Foo(x='1')
json_foo = foo.Schema().dumps(foo) # '{"x": "1"}'

# Back to class instance.
Foo.Schema().loads(json_foo) # Foo(x=1)

As a bonus for marshmallow_dataclass you may use validation on the field itself, that validation will be used when someone deserialize the object from json using that schema.

Dataclasses Json

from dataclasses import dataclass
from dataclasses_json import dataclass_json


@dataclass_json
@dataclass
class Foo:
    x: int

foo = Foo(x='1')
json_foo = foo.to_json() # Foo(x='1')
# Back to class instance
Foo.from_json(json_foo) # Foo(x='1')

Also, in addition to that notice that marshmallow dataclass did type conversion for you whereas dataclassses-json(ver.: 0.5.1) ignores that.

Write Custom Encoder

Follow accepted miracle2k answer and reuse custom json encoder.