Delete final line in file with python

You could use the above code and then:-

lines = file.readlines()
lines = lines[:-1]

This would give you an array of lines containing all lines but the last one.

This doesn't use python, but python's the wrong tool for the job if this is the only task you want. You can use the standard *nix utility head, and run

head -n-1 filename > newfile

which will copy all but the last line of filename to newfile.

Because I routinely work with many-gigabyte files, looping through as mentioned in the answers didn't work for me. The solution I use:

with open(sys.argv[1], "r+", encoding = "utf-8") as file:

    # Move the pointer (similar to a cursor in a text editor) to the end of the file
    file.seek(0, os.SEEK_END)

    # This code means the following code skips the very last character in the file -
    # i.e. in the case the last line is null we delete the last line
    # and the penultimate one
    pos = file.tell() - 1

    # Read each character in the file one at a time from the penultimate
    # character going backwards, searching for a newline character
    # If we find a new line, exit the search
    while pos > 0 and file.read(1) != "\n":
        pos -= 1
        file.seek(pos, os.SEEK_SET)

    # So long as we're not at the start of the file, delete all the characters ahead
    # of this position
    if pos > 0:
        file.seek(pos, os.SEEK_SET)
        file.truncate()