i got error while writing data to file

[Madhusudhanan Sambath]

hi to all,
this is madhu...i am new to python

this is my python code, where i labeled the reviews taken from amazon as positive, negative and neutral based on review score

i have collected reviews and scores from amazon scrap prg, but i have problem while doing labelling.kindly help me

import nltk
import csv
import ast

data=[]
positivedata=[]
negativedata=[]
neutraldata=[]




with open('E:/amadown2py-master/reviews1.csv', 'r',encoding='UTF8') as csvfile:
    mycsv = csv.reader(csvfile)
    for row in mycsv:
        data = row[0]
        #print (data)
        try:
            score = ast.literal_eval(row[1])
            if score > 3:
                cnt=0;
                #print (score)
                print (data)
                positivedata.append((data))
                with open('E:/amadown2py-master/Sam7_pos_rev.txt',mode='wt') as myfile:
                    myfile.writelines('\n'.join(positivedata))
                    myfile.close()


the above program is able to create file but full reviews are not read from csv . if i print the details about 48kb size, i got more data , but in file it have only 3kb why?kinldy help me