decode JSON in python

Question

I am having a problem I can't quite seem to find the solution to. I have an application that speaks with a Java app via JSON. Pretty simple, but I'm having an issue decoding JSON off the wire with nested objects. For example I have:

class obj1(object):
    def __init__(self, var1, var2):
        self.var1 = var1
        self.var2 = var2

    def __eq__(self, other):
      return (isinstance(other, obj1) and
        self.var1 == obj1.var1 and
        self.var2 == obj2.var2)

class obj2(object):
    def __init__(self, v1, v2, obj1):
        self.v1 = v1
        self.v2 = v2
        self.obj1 = obj1

and I want to serialize and de-serialize the "obj2" class, I can create it pretty easily:

myObj1 = obj1(1,2)
myObj2 = obj2(3.14, 10.05, myObj1)

when I want to send it Json, it's obviously pretty easy:

import json

def obj_to_dict(obj):
    return obj.__dict__

my_json = json.dumps(myObj2, default=obj_to_dict)

this creates the perfect JSON as I would expect:

{"obj1": {"var1": 1, "var2": 2}, "v1": 3.14, "v2": 10.05}

the problem I am having is encoding this string back into the two objects. I can't add any extra type information because the application that sends this schema back sends it back in exactly this way. so when I try and rebuild it from the dictionary:

obj_dict = json.loads(my_json)
myNewObj = obj2(**obj_dict)

it doesn't quite work

print myNewObj.obj1 == obj1  #returns False.

Is there some better way to get from JSON -> Custom objects? (In reality I have like 20 custom objects nested inside another Object. the Object -> JSON works perfectly, its just going the other direction. Any thoughts?

Have you tried adding debug output in def __eq__(self, other): ? — Finch_Powers
– Finch_Powers, Commented Nov 11, 2015 at 17:41
yes, basically what happens myNewObj.obj1 is a dictionary of the attributes and never gets instantiated into an "obj1" object with the right parameters. — user1772250
– user1772250, Commented Nov 11, 2015 at 17:46

Finch_Powers · Accepted Answer · 2015-11-11 17:51:37Z

2

You need to "chain" the object creation.

class obj2(object): def __init__(self, v1, v2, obj1): self.v1 = v1 self.v2 = v2 if type(obj1) is dict: self.obj1 = obj1(**obj1) else: self.obj1 = obj1

answered Nov 11, 2015 at 17:51

Finch_Powers

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user1494994 · Accepted Answer · 2015-11-11 18:54:49Z

I have a slightly different approach which uses inheritance:

class json_dict(object):
    def __init__(self, **kargs):
        self.dict = { k:kargs[k] for k in kargs.keys() }

    @property
    def json(self):
        d = self.dict
        return str({k:(d[k].dict if isinstance(d[k], json_dict) else d[k]) for k in d.keys()})


class obj1(json_dict):
    def __init__(self, var1, var2):
        super(obj1, self).__init__(var1=var1, var2=var2)  # dict at obj1 level

    def __eq__(self, other):
      return (isinstance(other, json_dict)) and (self.dict == other.dict)

class obj2(json_dict):
    def __init__(self, v1, v2, **kobjs):
        super(obj2, self).__init__(v1=v1, v2=v2)  # dict at obj2 level

        for k, obj in kobjs.iteritems():
            if isinstance(obj, json_dict):
                self.dict[k] = obj  # append as many objects as you need

With this approach, you can init obj1 and obj2 as followings:

myobj1 = obj1("obj1 variable 1","obj1 variable 2")
myobj2 = obj2("obj2 variable 1","obj2 variable 2", obj1=myobj1)

appendedmore = obj2("obj2 variable 1","obj2 variable 2", obj1=o1, obj2=o2, obj3=o3)  # o1,o2,o3 must inherit from json_dict

# get json string from the objects
myobj1.json  # "{'var1': 'obj1 variable 1', 'var2': 'obj1 variable 2'}"
myobj2.json  # "{'obj1': {'var1': 'obj1 variable 1', 'var2': 'obj1 variable 2'}, 'v1': 'obj2 variable 1', 'v2': 'obj2 variable 2'}"

Sorry if my code looks clunky! Please advice if have any suggestions!

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