Method __len__

django/forms/models.py:1452–1456

(self)

            yield self.choice(obj)

    def __len__(self):
        # count() adds a query but uses less memory since the QuerySet results
        # won't be cached. In most cases, the choices will only be iterated on,
        # and __len__() won't be called.
        return self.queryset.count() + (1 if self.field.empty_label is not None else 0)

    def __bool__(self):
        return self.field.empty_label is not None or self.queryset.exists()