f = open('my.pickle', 'ab')

class ID(object):
     def __init__(self, entity):
        self.entity_class = entity.__class__
        self.entity = entity
        objects[ID].append(self)
        if self.entity_class not in objects.keys():
            objects[self.entity_class] = []
            objects[self.entity_class].append(self.entity)
        else:
            objects[self.entity_class].append(self.entity)

objects = {ID:[]}

class Entity():
    fields_preset = []
    relations_preset = []
    def __init__(self):
        self.entity_id = ID(self)
        self.fields = []
        self.relations = []

t =type("NewType", (Entity,), {"x": "hello"})
t()
pickle.dump(objects, f, 2)