Concenating to every value in a list

Question

So I have a file with some lines of text:

here's a sentence
look! another one
here's a third one too
and another one
one more

and I have some code that takes the each line and puts it into a list and then reverses the order of the whole list but now I don't know how to write each line back to the file and delete the existing ones in the text file.

Also when I run this code:

file_lines = open(file_name).readlines()
print(file_lines)
file_lines.reverse()
print(file_lines)

everything works and the line order is reversed, but when I run this code:

text_file = open(file_name, "w")
file_lines = open(file_name).readlines()
print(file_lines)
file_lines.reverse()
print(file_lines)
for line in file_lines:
    text_file.write(line)

it prints empty lists for some reason.

Answer 1

You can fix it by doing just 2 little changes in your script.

1. Use \r+ in place of \w+

2. Before performing write operation, place file position indicator to the beginning

   text_file.seek(0)

» rw_file.txt - before operation

here's a sentence
look! another one
here's a third one too
and another one
one more

Below is your modified script to reverse the content of file (It worked).

def reverseFile(file_name):
    text_file = open(file_name, "r+") # Do not use 'w+', it will erase your file content 
    file_lines = [line.rstrip('\n') for line in text_file.readlines()]
    file_lines.reverse()
    print(file_lines)

    text_file.seek(0) # Place file position indicator at beginning

    for line_item in file_lines:
        text_file.write(line_item+"\n")


reverseFile("rw_file.txt")

» rw_file.txt - after operation

one more
and another one
here's a third one too
look! another one
here's a sentence