Editing a line in a file using Python

happysnake793

I am trying to edit a line in a file using Python. I have the line number, but I can't seem to get the line to change. Can anyone help?I'm trying to edit a line in a file using Python. I have the line number, but I can't seem to get the line to change. Can anyone help?

whitedog

Assuming you want to edit an existing line in a file, and not add a new line, you can do so with the following code:

with open("file.txt", "r+") as f:
    lines = f.readlines()
    lines[0] = "new line"
    f.seek(0)
    f.writelines(lines)

This will read all the lines in the file into a list, replace the line at index 0 with the string "new line", and then write the entire list back to the file, effectively replacing the original line.

brownwolf455

Assuming you would like to know how to edit a specific line in a text file using Python, below is an example.

Say you have a text file named "input.txt" with the following contents:

1 first line
2 second line
3 third line
4 fourth line
5 fifth line
6 sixth line

To edit the third line, you would first need to open the file in read/write mode:

f = open("input.txt", "r+")

Then, you would need to read in the file contents:

contents = f.readlines()

Now, you can edit the third line by simply reassigning the element in the "contents" list:

contents[2] = "3 edited third line\n"

Finally, you can write the "contents" list back out to the file:

f.seek(0)
f.writelines(contents)
f.close()

If you open "input.txt" back up, you should now see that the third line has been changed:

1 first line
2 second line
3 edited third line
4 fourth line
5 fifth line
6 sixth line