Encoding nested python object in JSON

my previous sample, with another nested object and your advices :

import json

class Identity:
    def __init__(self):
        self.name="abc name"
        self.first="abc first"
        self.addr=Addr()
    def reprJSON(self):
        return dict(name=self.name, firstname=self.first, address=self.addr) 

class Addr:
    def __init__(self):
        self.street="sesame street"
        self.zip="13000"
    def reprJSON(self):
        return dict(street=self.street, zip=self.zip) 

class Doc:
    def __init__(self):
        self.identity=Identity()
        self.data="all data"
    def reprJSON(self):
        return dict(id=self.identity, data=self.data) 

class ComplexEncoder(json.JSONEncoder):
    def default(self, obj):
        if hasattr(obj,'reprJSON'):
            return obj.reprJSON()
        else:
            return json.JSONEncoder.default(self, obj)

doc=Doc()
print "Str representation"
print doc.reprJSON()
print "Full JSON"
print json.dumps(doc.reprJSON(), cls=ComplexEncoder)
print "Partial JSON"
print json.dumps(doc.identity.addr.reprJSON(), cls=ComplexEncoder)

produces the expected result :

Str representation
{'data': 'all data', 'id': <__main__.Identity instance at 0x1005317e8>}
Full JSON
{"data": "all data", "id": {"name": "abc name", "firstname": "abc first", "address": {"street": "sesame street", "zip": "13000"}}}
Partial JSON
{"street": "sesame street", "zip": "13000"}

Thanks.