Using python to delete lines from a text fie

Question

Let's say I have a text file full of random lines. How can I keep a specific line and delete the others from this file, using Python? The script should search for all .txt files from a directory/and sub directory.

Answer 1

Firstly, to search for all .txt files, you can use this:

import glob, os
os.chdir("/mydir")
for filePath in glob.glob("*.txt"):
    ...

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Secondly, to look through a file and find the line you want, use:

 myfile = open(filePath, "r")

And look to see if your desired line is in the file.

if desiredLine in myfile:
    ...

Then you can close the file and reopen it in write mode.

myfile.close()
myfile = open(filePath, "w")

Then all you have to do is write the line you wanted to keep.

myfile.write(desiredLine)

Then close the file again

myfile.close()

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The final script ends up like this:

import glob, os
os.chdir("/mydir")
for filePath in glob.glob("*.txt"):
    myfile = open(filePath, "r")
    if desiredLine in myfile:
        myfile.close()
        myfile = open(filePath, "w")
        myfile.write(desiredLine)
    myfile.close()

Note, if your line doesn't exist in the file you're checking, it is left as is.

Hope this helps you