when we need methods groupped together

light_model.py

# coding: utf-8
from datetime import datetime
try:
    import simplejson as json
except ImportError:
    import json


datetime_json_handler = lambda obj: obj.isoformat() if isinstance(obj, datetime) else None


class ModelManager(object):

    def __init__(self):
        self.registered = {}

    def register(self, model):
        assert isinstance(model, Model)
        self.registered[model.__class__.__name__.lower()] = model

    def __getattr__(self, item):
        model = self.registered.get(item.lower(), None)
        if not model:
            raise AttributeError("model %s not registered" % item.capitalize())
        return model


class Model(object):

    def to_json(self, data):
        return json.dumps(data, default=datetime_json_handler)


class Project(Model):
    pass


class Category(Model):
    pass


class Source(Model):
    pass


class Gist(Model):
    pass


class Event(Model):
    pass


models = ModelManager()
models.register(Project())
models.register(Category())
models.register(Source())
models.register(Gist())
models.register(Event())