python method to handle null values in csv

# -*- coding: UTF-8 -*-
import 
import tensorflow as tf
import pandas as pd
import csv
import math
"""
1.Must be acquiredCSVFolder（ID：copies）
2.come (or go) back(ID：分词后的copies)
"""
flags = 
flags.DEFINE_string("train_file_address","D:/NLPWORD/cut_word_test/","Add training data file")
flags.DEFINE_string("result_file_address","D:/NLPWORD/cut_word_test/hzytest_result.csv","Generation of resultant data files")
FLAGS = 
def cut_word(train_data):
 """
 Iterate the data by rows and write the results by rows in a csv
 :return:Segmentation results list
 """
 jieba.load_userdict("")
 with open(FLAGS.result_file_address, "w", encoding='utf8') as csvfile:
 writer = (csvfile)
 for row in train_data.index:
  datas = train_data.loc[row].values[1]
  if isinstance(datas,str) or not (datas):
  words = (datas)
  line = ''
  for word in words:
   line = line +  + " "
  ([train_data.loc[row].values[0], line])
def main(_):
 data = pd.read_csv(FLAGS.train_file_address)
 cut_word(data)

if __name__ == "__main__":
 (main)