JSON serialization of dictionary with complex objects

Question

I am trying to serialize the dictionary playersElo for saving/loading it as/from JSON.

But as it's not a serializable object and I can't find a way to do it.

playersElo={} # dictionary of {<int> : <PlayerElo>}
playersElo[1] = PlayerElo()
playersElo[2] = PlayerElo()
...

class PlayerElo:
    """
    A class to represent a player in the Elo Rating System
    """
    def __init__(self, name: str, id: str, rating):
        self.id = id
        self.name = name
        # comment the 2 lines below in order to start with a rating associated
        # to current player rank
        self.eloratings = {0: 1500}
        self.elomatches = {0: 0}
        self.initialrating = rating

You could write out the object's `__dict__` to your JSON, and postprocess it on readback, or use `pickle` to convert it to something that be recreated later. — Tim Roberts, Dec 29 '21 at 22:55
Does this answer your question? [How to make a class JSON serializable](https://stackoverflow.com/questions/3768895/how-to-make-a-class-json-serializable) — mkrieger1, Dec 30 '21 at 00:28

score 1 · Accepted Answer · edited Jan 08 '22 at 12:16

Maybe this can be a starting spot for you. The serializer grabs the __dict__ attribute from the object and makes a new dict-of-dicts, then writes it to JSON. The deserializer creates a dummy object, then updates the __dict__ on the way in.

import json

class PlayerElo:
    """
    A class to represent a player in the Elo Rating System
    """
    def __init__(self, name: str, id: str, rating):
        self.id = id
        self.name = name
        self.eloratings = {0: 1500}
        self.elomatches = {0: 0}
        self.initialrating = rating


playersElo={} # dictionary of {<int> : <PlayerElo>}
playersElo[1] = PlayerElo('Joe','123',999)
playersElo[2] = PlayerElo('Bill','456',1999)

def serialize(ratings):
    newdict = {i:j.__dict__ for i,j in ratings.items()}
    json.dump( newdict, open('x.json','w') )

def deserialize():
    o = json.load(open('x.json'))
    pe = {}
    for k,v in o.items():
        obj = PlayerElo('0','0',0)
        obj.__dict__.update( v )
        pe[int(k)] = obj
    return pe

print(playersElo)
serialize( playersElo )
pe = deserialize( )
print(pe)

Thanks !! Just a correction here: obj.__dict__.update(**v**) #v here not o I think — user3497492, Dec 29 '21 at 23:56

score 1 · Answer 2 · edited Jan 08 '22 at 12:16

You can extend the json.JSONEncoder to handle instances of your class. There are examples in the module's documentation, but here one why of doing it with your PlayerElo class.

Note: Also see my answer to the question Making object JSON serializable with regular encoder for a more generic way of doing it.

import json


class PlayerElo:
    """ A class to represent a player in the Elo Rating System. """

    def __init__(self, name: str, id: str, rating):
        self.id = id
        self.name = name
        # comment the 2 lines below in order to start with a rating associated
        # to current player rank
        self.eloratings = {0: 1500}
        self.elomatches = {0: 0}
        self.initialrating = rating


class MyJSONEcoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, PlayerElo):
            return dict(type='PlayerElo', name=obj.name, id = obj.id,
                        rating=obj.initialrating)
        return super().default(obj)


playersElo={} # dictionary of {<int> : <PlayerElo>}
playersElo[1] = PlayerElo('Bob', 'thx1138', 4)
playersElo[2] = PlayerElo('Sue', 'p-138', 3)

from pprint import pprint
my_encoder = MyJSONEcoder()
pprint(my_encoder.encode(playersElo))

Here the JSON string it generated and printed:

('{"1": {"type": "PlayerElo", "name": "Bob", "id": "thx1138", "rating": 4}, '
 '"2": {"type": "PlayerElo", "name": "Sue", "id": "p-138", "rating": 3}}')

JSON serialization of dictionary with complex objects

2 Answers2