Delete the last line of a txt file

Question

I need to delete the last line of a txt file.

I found the last line like this:

with open('arquivo.txt', 'r') as content:
    line = content.readlines()
    last_line = line[len(line)-1]

Note: you can change the read mode in the open function.

Answer 1

If it is a very large file, see this form, it reads the file backwards in binary until it finds the character of the last line. Then convert him.

import os

with open('arquivo.txt', 'rb') as f:
   f.seek(-2, os.SEEK_END)
   while f.read(1) != b'\n':
      f.seek(-2, os.SEEK_CUR) 
   print(f.readline().decode())

Answer 2

To work with large files this is a possible solution:

import os

with open('arquivo.txt', 'r+', encoding = "utf-8") as arquivo:

    # Move o ponteiro (similar a um cursor de um editor de textos) para o fim do arquivo. 
    arquivo.seek(0, os.SEEK_END)

    # Pula o ultimo caractere do arquivo
    # No caso de a ultima linha ser null, deletamos a ultima linha e a penúltima
    pos = arquivo.tell() - 1

    # Lê cada caractere no arquivo, um por vez, a partir do penúltimo
    # caractere indo para trás, buscando por um caractere de nova linha
    # Se encontrarmos um nova linha, sai da busca
    while pos > 0 and arquivo.read(1) != "\n":
        pos -= 1
        arquivo.seek(pos, os.SEEK_SET)

    # Enquanto não estivermos no começo do arquivo, deleta todos os caracteres para frente desta posição
    if pos > 0:
        arquivo.seek(pos, os.SEEK_SET)
        arquivo.truncate()

Answer 3

If we happen to be on *Nix systems, a solution would be

head -n -1 file > novo

... but does not use Python.

Answer 4

In this way:

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