How to convert serialized JSON generated in Java to complex object in Python?

Question

I have defined two classes in Java. Let's call them 'User' and 'Address'

class Address {
    String addressFirstLine;
    String city;
    String pincode;

    // Getters/setters for all attributes
}

class User {
    String firstName;
    String lastName;
    Address address;

    // Getters/setters for all attributes
}

I created an object of class User and serialized it using Gson library.

The JSON String looks something like:

{"firstname":"Zen","lastName":"coder", "Address":{"addressFirstLine":"High st, Point place","city":"Wisconcin","pincode":"4E23C"}}

Now this string is sent to a python application which have the same two class definitions 'User' and 'Address' defined exactly like in Java above.

I have tried deserializing the json to a python object using jsonpickle. I can deserialize simple objects with jsonpickle but not complex objects.

Could anyone suggest a way around this?

just added what the JSON would look like after serialisation using Gson in Java. see edits. — zenCoder
– zenCoder, Commented Apr 2, 2013 at 14:57
How about simply writing the custom classemethod .fromJSON on both of these classes? — freakish
– freakish, Commented Apr 2, 2013 at 14:57
I'm not familiar with JSONPickle, but there must be a python library that can do what you require... What does google say? — RudolphEst
– RudolphEst, Commented Apr 2, 2013 at 14:58

Community · Accepted Answer · 2017-05-23 12:03:20Z

2

This may be a solution for you using Python built-in JSON library that takes advantage of Python's ability to ingest dictionaries as keyword arguments.

I defined the classes in Python as I would expect based on your outline. In the User class definition, I allow address to be passed as an actual address object, a list (converted from a JSON Array), or a dictionary (converted from a JSON object).

class Address(object):
def __init__(self, addressFirstLine, city, pincode):
    self.addressFirstLine = addressFirstLine
    self.city = city
    self.pincode = pincode


class User(object):
    def __init__(self, firstName, lastName, address):
        self.firstName = firstName
        self.lastName = lastName
        if isinstance(address, Address):
            self.address = address
        elif isinstance(address, list):
            self.address = Address(*address)
        elif isinstance(address, dict):
            self.address = Address(**address)
        else:
            raise TypeError('address must be provided as an Address object,'
            ' list, or dictionary')

I use the built-in Python json library to convert the JSON string you provided to a dictionary, then use that dictionary to create a user object. As you can see below, user.address is an actual Address object (I defined User and Address inside a file called user_address.py, hence the prefix).

>>> import json
>>> user_dict = json.loads('{
    "firstName" : "Zen", "lastName" : "Coder", 
    "address" : {
        "addressFirstLine" : "High st, Point place",
        "city" : "Wisconcin", 
        "pincode" : "4E23C"}
    }')
>>> from user_address import User
>>> user = User(**user_dict)
>>> user
    <user_address.User at 0x1035b4190>
>>> user.firstName
    u'Zen'
>>> user.lastName
     u'coder'
>>> user.address
     <user_address.Address at 0x1035b4710>
>>> user.address.addressFirstLine
    u'High st, Point place'
>>> user.address.city
    u'Wisconcin'
>>> user.address.pincode
    u'4E23C'

This implementation also supports having a list of address arguments as opposed to a dictionary. It also raises a descriptive error if an unsupported type is passed.

>>> user_dict = json.loads('{
    "firstName" : "Zen", "lastName" : "coder", 
    "address" : ["High st, Point place", "Wisconcin", "4E23C"]
    }')
>>> user = User(**user_dict)
>>> user.address
    <user_address.Address at 0x10ced2d10>
>>> user.address.city
    u'Wisconcin'
>>> user_dict = json.loads('{
    "firstName" : "Zen", "lastName" : "coder", 
    "address" : "bad address"
    }')
    TypeError: address must be provided as an Address object, list, or dictionary

This other answer also talks about converting a Python dict to a Python object, with a more abstract approach: Convert Python dict to object

edited May 23, 2017 at 12:03

CommunityBot

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answered Apr 2, 2013 at 21:31

Jacinda

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4 Comments

zenCoder Over a year ago

Thanks a lot for the example. Sounds like the right approach. Before I mark it as the answer, could you tell me if the above approach would work if 'address' were an Array of type Address?

Jacinda Over a year ago

It won't work as currently written, but I can modify it to do what I think you're asking. Would this be an example of the JSON in this case? {"firstName":"Zen","lastName":"coder", "address":["High st, Point place", "Wisconcin", "4E23C"]} If not, please provide me an example.

Jacinda Over a year ago

Updated based on what I think you were asking about Arrays. Let me know if this is what you were wondering.

zenCoder Over a year ago

Actually, I'm warming up to dictionaries. I don't think I need to create objects now. Think it'll work out fine. Thanks everyone!

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