Python - delete blank lines of text at the end of the file

Question

I am writing a script that modifies any text files. It replaces white space lines with blank lines. It erases the blank lines at the end of the file. The image shows the output I want.

I am able to get very close to the desired output. The problem is that I cannot get rid of the last blank line. I think this has something to do with the last line. e.g ' the lines below me should be gone actually looks like this ' the lines below me should be gone\n' It looks like new lines are created on the previous line. e.g if line 4 has \n than line 5 will actually be the blank line not line 4.

I should note that I can't use rstrip or strip

My code so far.

def clean_file(filename):
    # function to check if the line can be deleted
    def is_all_whitespace(line):
        for char in line:
            if char != ' ' and char != '\n':
                return False
        return True

    # generates the new lines
    with open(filename, 'r') as file:
        file_out = []
        for line in file:
            if is_all_whitespace(line):
                line = '\n'
            file_out.append(line)

    # removes whitespaces at the end of file
    while file_out[-1] == '\n':  # while the last item in lst is blank
        file_out.pop(-1)  # removes last element

    # writes the new the output to file
    with open(filename, 'w') as file:
        file.write(''.join(file_out))

clean_file('test.txt')

Answer 1

The \n essentially means "create another line"

So when you've removed all the lines that are \n, there's still the preceding line

the lines below me should be gone\n

Which again means "create another line", beyond the ones you've already removed

Since you say you can't use rstrip, you could end the loop with

file_out[-1] = file_out[-1].strip('\n')

to remove \n from the last element. Because \n can't exist anywhere else in a line, rstrip and strip will have the same effect

Or without any strip or endswith:

if file_out[-1][-1] == '\n':
    file_out[-1] = file_out[-1][:-1]

Note that \n is a single character, ordinal 0x0a as hex, not two characters \ and n, ordinals 0x5c and 0x6e. That is why we use -1 and not -2