code: def _write_header(self, fd: TextIO):
      csvwriter = csv.DictWriter(
          fd, fieldnames=self.fieldnames, delimiter=self.separator
      )
      csvwriter.writeheader()
  
imports: import csv
  import os
  from typing import Dict, List, Optional, TextIO, Union
  import torch
  from poutyne.framework.callbacks._utils import atomic_lambda_save
  from poutyne.framework.callbacks.callbacks import Callback
label_desc: Use image node_id 3 for calling the AtomicCSVGradientLogger obj's underlying member method code with example usage: obj._write_header(fd) without return types