code: def zero_grad(variables):
      for variable in variables:
          variable.grad.zero_()
  
imports: import numpy
  import torch
  import pytest
  import random
  import copy
  import os
  from torch import nn
  from deepspeed import DeepSpeedTransformerLayer, DeepSpeedTransformerConfig
  from deepspeed.accelerator import get_accelerator
  from unit.modeling import BertConfig, BertLayerNorm, BertEncoder
  from unit.modelingpreln import BertEncoder
  from unit.common import DistributedTest, is_rocm_pytorch
label_desc: Use image node_id 2 for calling a global function with example usage: zero_grad(variables) without return types