code: def _grad_var_from_alive_node(node):
      # Used by `accumulate_grad_inputs` option of `GradTable`
      var = node.get_variable_or_none()
      if var is None:
          return None
      else:
          gv = var.grad_var
          var.grad_var = None
          return gv
  
imports: import os
  import shutil
  import sys
  import traceback
  import six
  import chainer
label_desc: Use image node_id 4 for calling a global function with example usage: _grad_var_from_alive_node(node) and returns: None, gv