code: def test_single_kv_pair():
      """single key-value pair push & pull"""
  
      def check_single_kv_pair(kv, key, stype):
          kv.push(key, mx.nd.ones(shape).tostype(stype))
          val = mx.nd.empty(shape)
          kv.pull(key, out=val)
          check_diff_to_scalar(val, 1)
  
      stypes = ["default", "row_sparse"]
      for stype in stypes:
          check_single_kv_pair(init_kv(), 3, stype)
          check_single_kv_pair(init_kv_with_str(), "a", stype)
  
imports: import mxnet
  import numpy
  import unittest
  from mxnet.test_utils import rand_ndarray, assert_almost_equal
  from common import assertRaises
  from mxnet.base import py_str, MXNetError
  import pytest
label_desc: Use image node_id 4 for calling a global function with example usage: test_single_kv_pair() without return types