write function not working properly in python

Question

I wrote a code to produce the following output. It works fine when I use append function in marked line in code but when i use ''w' write function it, it only prints one line in the new created text file. Problem to use append function is if we run the code again it copies same output twice. I am not able to understand this . Please Help Thanks in advance

Code I used:

import os
with open("input5.csv", 'r+') as fd:
    lines = fd.readlines()
    fd.seek(0)
    fd.writelines(line for line in lines if line.strip())
    fd.truncate()

lines = open('input5.csv').readlines()
open('output1.txt', 'w').writelines(lines[1:-2])

with open('output1.txt', 'r+') as m:
    newText = m.read()
    while ',' in newText:
        newText = newText.replace(',', '_')
with open('output1.txt', "w") as m:
    m.write(newText)

with open("output1.txt","r+") as fp:
    for cnt, line in enumerate(fp):
        line=line.replace('_',',',3)
        print(line)
        f = open('output7.txt', 'a') #THIS LINE
        for i in range(len(line)):
            f.write((line[i]))
        f.close()
os.remove("output1.txt")

Input:

id,name,amount,subject
1,abc,55,"s1,s2,s3"
1,abc1,56,"s4,s5,s6"
1,abc2,57,"s7,s8,s9"
1,abc3,58,"s10,s11,s12"
1,abc4,59,"s13,s14,s15"
1,abc5,59,"s16,s17,s18"
1,abc6,59,"s13,s14,s15"
1,abc7,59,"s13,s14,s15"
1,abc8,59,"s13,s14,s15"
1,abc9,59,"s13,s14,s15"
this file is done
time taken; 22nd

expected output:(This is the code i get when use append function marked line of the code)

1,abc,55,"s1_s2_s3"
1,abc1,56,"s4_s5_s6"
1,abc2,57,"s7_s8_s9"
1,abc3,58,"s10_s11_s12"
1,abc4,59,"s13_s14_s15"
1,abc5,59,"s16_s17_s18"
1,abc6,59,"s13_s14_s15"
1,abc7,59,"s13_s14_s15"
1,abc8,59,"s13_s14_s15"
1,abc9,59,"s13_s14_s15"

Output i get when I replace append with write function in marked line of code:

1,abc9,59,"s13_s14_s15"

You should only open the file for writing one time, before the loop, and close it after the loop. — Stefan
– Stefan, Commented May 31, 2019 at 10:59
@Stefan if possible can you edit the code. It will be of great help. — udit kanotra
– udit kanotra, Commented May 31, 2019 at 11:03

Stefan · Accepted Answer · 2019-05-31 11:03:47Z

1

Something like this (not tested), where the file open and close is outside the loop:

import os
with open("input5.csv", 'r+') as fd:
    lines = fd.readlines()
    fd.seek(0)
    fd.writelines(line for line in lines if line.strip())
    fd.truncate()

lines = open('input5.csv').readlines()
open('output1.txt', 'w').writelines(lines[1:-2])

with open('output1.txt', 'r+') as m:
    newText = m.read()
    while ',' in newText:
        newText = newText.replace(',', '_')
with open('output1.txt', "w") as m:
    m.write(newText)

with open("output1.txt","r+") as fp:
    f = open('output7.txt', 'w') #THIS LINE
    for cnt, line in enumerate(fp):
        line=line.replace('_',',',3)
        print(line)

        for i in range(len(line)):
            f.write((line[i]))
    f.close()
os.remove("output1.txt")

answered May 31, 2019 at 11:03

Stefan

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2 Comments

Stefan Over a year ago

You could use a with statement instead of the open-close pair, if you want

Ufos Over a year ago

I understand how this is not a great practice to open the file multiple times inside of a loop, but for some purposes this might be desired, and this code could be just a prototype of a much larger software framework in mind. So, how come, open with 'a'->write->close does not work as expected?

Ufos · Accepted Answer · 2019-05-31 11:37:27Z

1

On my machine (Ubuntu 18.04) with python 3.6.7 your example works as expected.

output7.txt contains

1,abc,55,"s1_s2_s3"
1,abc1,56,"s4_s5_s6"
1,abc2,57,"s7_s8_s9"
1,abc3,58,"s10_s11_s12"
1,abc4,59,"s13_s14_s15"
1,abc5,59,"s16_s17_s18"
1,abc6,59,"s13_s14_s15"
1,abc7,59,"s13_s14_s15"

So, the write function does work properly. However, it is a good question, why doesn't it work for you.

answered May 31, 2019 at 11:37

Ufos

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2 Comments

udit kanotra Over a year ago

sir i am using python on windows. I didn't test it on Ubuntu. Stefan's solution worked for me .

Ufos Over a year ago

Well, any solution that solves a problem is good. But you should be very concerned if something in the language does not work as expected. You might not notice, but 3+2 will be suddenly 1 because + works as -. So, when something like this happens it's a good practice to update to the latest stable version, check if the bug persists and then report to the devs.

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