How to remove a specific line that contains a specific string?

Question

I have tried some codes myself based off of codes I found online but none seems to be working.

The text file contains something as such:

Student ID: 1230345

Course code:FHCT1024
Grade: A
GPA: 4.0000

CGPA :4.0000

and I want to delete the line with the string 'CGPA' in it. I tried using:

with open("file.txt", 'r') as inp, open("file.txt", 'w') as f:
    for line in inp:
        if line.strip().startswith("CGPA"):
            pass
        else:
            f.write(line)

But this deleted everything.

Opening a file in `'w'` mode destroys the existing contents. — John Gordon, Dec 05 '20 at 16:23
You can't read and write to a file simultaneously (easily). Either write the results to a temporary file and rename it after deleting the original, or store the results in memory and rewrite the original file afterwards. — martineau, Dec 05 '20 at 16:26

score 1 · Accepted Answer · answered Dec 05 '20 at 16:23

You can filter the lines while you are reading the file

res = []

with open("file.txt", 'r') as inp:
            for line in inp:
                if line.strip().startswith("CGPA"):
                    pass
                else:
                    res += [line]

res will contain all the lines that do not start with "CGPA".

Once you have res , you can write it to a file if needed

score 1 · Answer 2 · edited Dec 05 '20 at 20:43

1

text='''Student ID: 1230345

Course code:FHCT1024
Grade: A
GPA: 4.0000

CGPA :4.0000'''

text_ls=text.splitlines()

for i in range(len(text_ls[:])):
    if text_ls[i].startswith('CGPA'):
        text_ls.remove(text_ls[i])
print('\n'.join(text_ls))

edited Dec 05 '20 at 20:43

Dharman

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answered Dec 05 '20 at 16:26

Yash Makan

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yes this gave a clear concept thanks man – William Dec 06 '20 at 12:58

score 1 · Answer 3 · answered Dec 05 '20 at 16:28

1

If the only purpose of your program is delete the line starting with CGPA, I would suggest you to look at sed command.

sed '/^CGPA/d' file.txt

This is much faster and needs lesser number of lines of code.

answered Dec 05 '20 at 16:28

bigbounty

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I will have a look into sed thanks – William Dec 06 '20 at 12:56

score 0 · Answer 4 · answered Dec 05 '20 at 16:25

0

Let's open in append mode ('a'):

with open("file.txt", 'r') as inp, open("file.txt", 'a') as f:
            for line in inp:
                if line.strip().startswith("CGPA"):
                    pass
                else:
                    f.write(line)

answered Dec 05 '20 at 16:25

Wasif

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This appended the text without the CGPA line so if it was in write mode it would work i think thanks. – William Dec 06 '20 at 13:02

score 0 · Answer 5 · answered Dec 05 '20 at 16:25

So the problem is that youre reading to the same file youre writing, this can lead to problems, because as youre reading the file the data is changing and is dynamic. Then you can try naming the file youre writing on differently. Here you have your input file named file.txt. Then name your output file "fileoutput.txt".

Also you can search for different opening file modes such as '+r' and others that can make this process easier.

But this should work:

with open("file.txt", 'r') as inp, open("fileoutput.txt", 'w') as f:
            for line in inp:
                if line.strip().startswith("CGPA"):
                    pass
                else:
                    f.write(line)

score 0 · Answer 6 · answered Dec 05 '20 at 16:41

If you need to read, update, then write; I would recommend breaking that up into two distinct open context managers: one for read and one for write because flat is easier to grok than nested. Also, you may want to write to a different file in order to preserve the original.

lines_without_cgpa = []

with open("file.txt", 'r') as f:
    for line in f.readlines():
        if "CGPA" not in line and "" != line:
            lines_without_cgpa.append(line)

print(lines_without_cgpa)

with open("file_without_cgpa.txt", 'w') as f:
    f.writelines(lines_without_cgpa)

How to remove a specific line that contains a specific string?

6 Answers6