def count(self):
        if self._result_cache is not None:
            return len(self._result_cache)

        return self.query.get_count(using=self.db)
Return the number of attributes in the scheme
dataset/ETHPy150Open django/django/django/db/models/query.py/QuerySet.count--crossover with--dataset/ETHPy150Open uwescience/raco/raco/scheme.py/Scheme.__len__