def __len__(self):
        return len(self._byname)
Given a Child model which also has an InheritanceManager,
dataset/ETHPy150Open natestedman/Observatory/observatory/lib/dulwich/index.py/Index.__len__--crossover with--dataset/ETHPy150Open carljm/django-model-utils/model_utils/tests/tests.py/InheritanceManagerUsingModelsTests.test_child_doesnt_accidentally_get_parent