class_docstr: CSV format benchmark writer.
  
  It writes benchmark statistics taken by :class:`FunctionBenchmark`
  in CSV file format.
  
  Args:
      file (Python file object): The benchmark will be written to the file.
class_docstr_tok: ["CSV","format","benchmark","writer",".","It","writes","benchmark","statistics","taken","by",":","class",":","`","FunctionBenchmark","`","in","CSV","file","format",".","Args",":","file","(","Python","file","object",")",":","The","benchmark","will","be","written","to","the","file","."]
code: def write_header(self):
      fields = [
          "module",
          "function",
          "class",
          "inspecs",
          "func_args",
          "func_kwargs",
          "ext",
          "ext_kwargs",
          "setup [ms/run]",
          "setup [run]",
          "forward [ms/run]",
          "forward [run]",
          "backward [ms/run]",
          "backward [run]",
      ]
      writer = csv.writer(self.file)
      writer.writerow(fields)
  
imports: from __future__ import print_function
  import nnabla
  import nnabla.initializer
  import sys
  import importlib
  import time
  from collections import namedtuple
  import csv
label_desc: Use image node_id 2 for calling the FunctionBenchmarkCsvWriter obj's underlying member method code with example usage: obj.write_header() without return types