code: def _update_params_on_kvstore(param_arrays, grad_arrays, kvstore, param_names):
      
      for index, pair in enumerate(zip(param_arrays, grad_arrays)):
          arg_list, grad_list = pair
          if grad_list[0] is None:
              continue
          name = param_names[index]
          # push gradient, priority is negative index
          kvstore.push(name, grad_list, priority=-index)
          # pull back the weights
          kvstore.pull(name, arg_list, priority=-index)
docs: Perform update of param_arrays from grad_arrays on kvstore.