Prototype for a serializable decimal field for Marshmallow

serializable_decimal.py

from decimal import Decimal
from marshmallow import Schema, ValidationError, fields, post_load


class SerializableDecimal(fields.Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if value is None:
            return None
        if not isinstance(value, Decimal):
            raise ValidationError("must be a Decimal value")
        return str(value)

    def _deserialize(self, value, attr, data, **kwargs):
        try:
            return Decimal(value)
        except Exception as error:
            raise ValidationError("cannot deserialize as Decimal") from error


class MyDecimal:
    dec: Decimal

    class Schema(Schema):
        dec = SerializableDecimal()

        class Meta:
            strict = True

        @post_load
        def objectify(self, data):
            return MyDecimal(**data)

    def __init__(self, dec: Decimal):
        self.dec = dec

    def __repr__(self):
        return f'MyDecimal(dec={self.dec})'

      
if __name__ == '__main__':
    my_dec = MyDecimal(Decimal('10.44244422008'))
    serialized = MyDecimal.Schema().dumps(my_dec).data
    print(serialized)

    deserialized = MyDecimal.Schema().loads(serialized).data
    print(deserialized)