code: def _scatter_add(a, index, v=1):
      index = index.tolist()
      for i in index:
          a[i] += v
      return a
  
imports: import unittest
  import warnings
  import backend
  import pytest
  import torch
  from dgl.sparse import diag, from_coo, from_csc, from_csr, from_torch_sparse, identity, to_torch_sparse_coo, to_torch_sparse_csc, to_torch_sparse_csr, val_like
  from .utils import rand_coo, rand_csc, rand_csr, rand_diag, sparse_matrix_to_dense
label_desc: Use image node_id 8 for calling a global function with example usage: _scatter_add(a, index, v) and returns: a