class_register = {}

class Foo(object):
    def __init__(self, **kwargs):
        class_register[self.__class__.__name__] = ??  # what to store here?
        self.__dict__.update(kwargs)

new_instance = class_register[result['class_name']](**result['data'])

class_register[self.__class__.__name__] = self.__class__

def register(cls):
    class_register[cls.__name__] = cls

class Foo(object):
    # blah blah

register(Foo)

def register(cls):
    class_register[cls.__name__] = cls
    return cls

@register
class Foo(object):
    # blah blah