Python Replace content in specific line at txt file

Question

I have a txt file with content as below: name password number location

the four items are separated into each line

I would like to change the content in the specific line, eg: change the third line("number") to "phone number"

Problem I faced is not replacing the "number", "number" still there, and the "phone number" is appended at the last line

Output:
name
password
number
location
phone number

How should I fix the code, so it can replace the content in certain line?

Below is my code

userID = 1

print("Modify: ")
print("1. Username")
print("2. Password")
print("3. Contact number")
print("4. Location")
print()
print("Enter 'main' to back to main screen")
select = int(input())
change = input("Change to: ")

if select != 'main:':
    if int(select) <= 4:
        #save to individual file
        fhand = open("user_"+str(userID)+".txt",'r+') 
        
        lineNo = 0 #line number
        for line in fhand(): 
            lineNo = lineNo + 1
            if lineNo == select:
                fhand.write(line.replace(line, change)) #replace the content
                print()
                print("Changed to:", change)
                print("Change successful")
                print("\n Bring you back to <customer main menu>")
 
        fhand.close()

I tried counting the line number, then when the line number reach the selection of the user, it starts to replace the line, and it doesn't work

Thanks for the helps

This is not the code you're running. The code you posted cannot run because of `for line in fhand(): ` - file is not callable, it raises an error. Please provide the code you're actually running — h4z3, Jun 17 '21 at 13:09
https://stackoverflow.com/questions/5453267/is-it-possible-to-modify-lines-in-a-file-in-place — Peter Wood, Jun 17 '21 at 13:15
Sidenote, `int(input())` before you check `if select != 'main'` is going to raise `ValueError` when you input `'main'`. — adamkwm, Jun 17 '21 at 13:20
Apologise that I removed .readlines and didn't notice `for line in fhand.readlines():` should be correct and running without error, just the output is incorrect. ya haven't test for giving input 'main', thanks for reminding — hijunxian0805, Jun 17 '21 at 13:27

Dakopen · Answer 1 · 2021-06-17T13:11:42.000

0

You can't edit or replace a single line in a file. Try to open a second file (e.g.newtext = open("newtext.txt", "a+") and do something like this:

for line in fhand.readlines():
    if line != select:
        newtext.write(line)
    else:
        line = line.replace(line, change)
        newtext.write(line)

also, try using with open as statements, for example

with open("newtext.txt", "a+") as newtext:
    for line in fhand.readlines():
        if line != select:
            newtext.write(line)
        else:
            line = line.replace(line, change)
            newtext.write(line)

edited Jun 17 '21 at 13:11

answered Jun 17 '21 at 13:09

Dakopen

62
11

That's false. Read+write mode serves exactly this purpose. It's just that OP posted wrong code (with error), so we can't even analyze what's wrong – h4z3 Jun 17 '21 at 13:11
You could do the reading and writing all in one like this https://pythonexamples.org/python-replace-string-in-file/ article suggests, but that's basically my solution without a second file. I thought, especially for beginners, it is easier to do it in separate files. – Dakopen Jun 17 '21 at 13:14
https://stackoverflow.com/questions/5453267/is-it-possible-to-modify-lines-in-a-file-in-place – Peter Wood Jun 17 '21 at 13:15

Edo Akse · Answer 2 · 2021-06-17T13:25:29.993

Quickest fix would be to read the whole file, close it, and rewrite with the correct data. This way you ensure that the new file has the correct contents.

I highly advise you to switch to using JSON files though. You won't have the same issue as you can load a JSON file as a dict, change the correct value, and rewrite the changed dict/JSON. Structured datafiles FTW...

Adjusting the current code, see below.

userID = 1

print("Modify: ")
print("1. Username")
print("2. Password")
print("3. Contact number")
print("4. Location")
print()
print("Enter 'main' to back to main screen")
select = int(input()) - 1 # offset difference between selection options and 0-based list
change = input("Change to: ")

if select != 'main:':
    if select < 4 and select >= 0:  # adjusted due to adjusting the select above
        filename = f'user_{str(userID)}.txt'
        # load file
        with open(filename) as infile:
            filecontents = infile.readlines()
        # make the change
        filecontents[select] = f'{change}\n'
        # save the result
        with open(filename, 'w') as outfile:
            outfile.writelines(filecontents)
        print()
        print("Changed to:", change)
        print("Change successful")
        print("\n Bring you back to <customer main menu>")

score 0 · Answer 3 · answered Jun 17 '21 at 13:20

the filemode r+ is reading and appending, so if you want to change the existing contents of the file then you have to open the file in write mode.

userID = 1

print("Modify: ")
print("1. Username")
print("2. Password")
print("3. Contact number")
print("4. Location")
print()
print("Enter 'main' to back to main screen")
select = int(input())
change = input("Change to: ")

if select != 'main:':
    if int(select) <= 4:
        #save to individual file
        with open("user_"+str(userID)+".txt",'r') as f:
            lines = f.readlines()
        # fhand = open("user_"+str(userID)+".txt",'r+') 
        
        lineNo = 0 #line number
        for line in lines: 
            lineNo = lineNo + 1
            if lineNo == select -1:
                lines[lineNo] = line.replace(line, f'{change}\n')
                with open("user_"+str(userID)+".txt",'w') as f:
                    f.write("".join(lines)) #replace the content
                print()
                print("Changed to:", change)
                print("Change successful")
                print("\n Bring you back to <customer main menu>")
                break
 
        # fhand.close()

I have taken the liberty to change some variable names; do change to your usecase accordingly.

score 0 · Accepted Answer · answered Jun 17 '21 at 13:21

0

Instead of that, what you can do is go with this code for editing the text file

with open(path_to_text_file,'r') as txt:
    text=txt.readlines()
    text[3]='phone number\n'

    with open(path_to_text_file,'w') as txt:
        txt.writelines(text)

answered Jun 17 '21 at 13:21

Bibekjit Singh

142
1
1
9

score 0 · Answer 5 · answered Jun 17 '21 at 13:23

slight modifications:

userID = 1

print("Modify: ")
print("1. Username")
print("2. Password")
print("3. Contact number")
print("4. Location")
print()
print("Enter 'main' to back to main screen")
select = int(input())-1
change = input("Change to: ")

if select != 'main:':
    if int(select) <= 4:
        # save to individual file
        with open("user_" + str(userID) + ".txt", 'r+') as file:
            data = file.readlines()
        for index, line in enumerate(data):
            if index == select:
                data[index] = line.replace(line, f"{change}\n")
                break
        with open("user_" + str(userID) + ".txt", 'r+') as file:
            file.writelines(data)
        print("Changed to:", change)
        print("Change successful")
        print("\n Bring you back to <customer main menu>")

Python Replace content in specific line at txt file

5 Answers5