JSON serialize objects in Python in list / diconary

The custom encoder class handles that for you when you use json.dumps(my_object, cls=MyCustomJsonEncoder). Your custom encoder would override the default method, which takes self and the object o to encode; test for the different types that need custom serialization, and pass the rest to the default with super(MyCustomJsonEncoder, self).default(o).

A simple example that I often use is as follows:

class JSONEncoder(json.JSONEncoder):
    """
    Enhancement of base JSONEncoder, also handling these objects:
     * datetime.datetime
     * decimal.Decimal
     * uuid.UUID
    """

    def default(self, o):
        if isinstance(o, Decimal):
            return float(o)
        elif isinstance(o, UUID):
            return str(o)
        elif isinstance(o, datetime):
            return {
                '__type__': 'datetime',
                '__value__': o.isoformat(),
            }
        return super(JSONEncoder, self).default(o)

    @staticmethod
    def dumps(obj):
        return json.dumps(obj, cls=JSONEncoder)

As Steven Wolfe stated in this thread, you may want to look into jsonpickle. This library allows for encoding and decoding of complex Python object.

You could use it this way:

import jsonpickle

f = open(filename, 'w')
encoded_string = jsonpickle.encode(obj)
f.write(encoded_string)
f.close()

And to retrieve the data as Python object, simply use the jsonpickle.decode(encoded_string) method. As the documentation says :

The new object has the same type and data, but essentially is now a copy of the original.

I think that could work well for you.