class PersonModel(object):
    _people = [
        {
            'name': {
                'first': 'Hammy',
                'last': 'Spammy',
            },
            'age': 42,
            'id': 1,
        },
        {
            'name': {
                'first': 'Sampers',
                'last': 'Dancer',
            },
            'age': 38,
            'id': 2
        },
    ]

    def __init__(self):
        self._index()

    def _index(self):
        self._people_by_id = dict(((p['id'], p) for p in self._people))

    def getall(self):
        return self._people

    def get(self, person_id):
        return self._people_by_id[person_id]

    def add(self, person):
        if None in (person.get('name'), person.get('age')):
            raise ValueError('Missing required fields!: {}'.format(person))

        person['id'] = len(self._people) + 1
        self._people.append(person)
        self._index()
        return person['id']