def test_invalid_scalar_index(adata, index):
    # https://github.com/theislab/anndata/issues/619
    with pytest.raises(IndexError, match=r".*index.* out of range\."):
        _ = adata[index]
def _getN(self, n):
        n -= 1
        p = self.head
        while n:
            p = p.next
            n -= 1
        return p