gistfile1.py

import json

class Foo(object):
  def __init__(self, **kwargs):
		self.__dict__.update(kwargs)


class MyEncoder(json.JSONEncoder):
	def default(self, obj):
		if isinstance(obj, Foo):
			return obj.__dict__
		return json.JSONEncoder.default(obj)

x = Foo(a=42, b=Foo(c=23))

print MyEncoder().encode(x)