Python: converting class objects to JSON - object is not JSON serializable-CodePudding

I have a list of objects in my Python code. Each object is of type Outer with associated Inner objects - the classes are defined like this:

from decimal import Decimal

@dataclass
class Inner:
    col_a: Decimal
    col_b: str
    col_c: List['str']

@dataclass
class Outer:
    col_a: str
    col_b: Decimal
    col_c: List[Inner]

I would like to convert these objects into JSON. As I am using Decimal, I was hoping to just create my own encoder and use it in conjunction with json.dumps():

class DecimalJsonEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Decimal):
            return str(obj)
        else:
            return super(DecimalJsonEncoder, self).default(obj)

... and...

my_json = json.dumps(my_list, cls=DecimalJsonEncoder)

However, when I create a list of Outer objects (my_list) and try to create JSON, I get this error:

TypeError: Object of type Outer is not JSON serializable

I'm using Python 3.7.

Thanks in advance for any assistance.

CodePudding user response：

You wish the encoder to support both Decimal and dataclasses. You can do it like so:

import dataclasses, json

class JSONEncoder(json.JSONEncoder):
        def default(self, o):
            if dataclasses.is_dataclass(o):
                return dataclasses.asdict(o)
            if isinstance(obj, Decimal):
                return str(obj)
            return super().default(o)

json.dumps(foo, cls=JSONEncoder)