How do I store data and not delete when the program ends?

Question

How do I make sure that when a data is stored, it is not deleted from the program ending? for example:

LISTA = ['Morango', 'Abacate']
ADD_ITEM = input('Digite algo que deseja adcionar:')
LISTA.append(ADD_ITEM)

While the program is running, the value is stored in LISTA. However, at the end of the program, the stored value simply disappears. How am I supposed to fix this?

I’ve tried the open, but as I don’t know how to use it very well, I ended up failing.

I’ve used every kind of list.

Answer 1

You need to save this list to a file, and read this file when you run the program (if it exists).

The hardest part of doing this is translating your data into a file and vice versa. I’ll show you 3 methods here, in a more or less didactic progression, I hope it helps.

METHOD 1

In your case, which is just a list of strings, we can organize in a simple way by saving a file with each element in a row. You would then have:

LISTA = ['Morango', 'Abacate']

That turns the file "LIST.txt":

Morango
Abacate

Remember that a line break is actually a special character \n, then in fact the contents of the file is:

Morango\nAbacate\n

With that in mind, let’s go to the code. It’s well commented for you to follow:

import os

LISTA = []

## Carrega a lista do arquivo
# Abre o arquivo (se ele já existe)
if os.path.exists("LISTA.txt"):
    # Abre o arquivo para leitura ('r' -> read)
    file = open("LISTA.txt", 'r')
    # Lê o arquivo linha por linha e coloca na lista
    for item in file.readlines():
        LISTA.append(item[:-1]) # Esse [:-1] tira o último caractere, um "\n"
    # Fecha o arquivo
    file.close()

## Seu código
ADD_ITEM = input('Digite algo que deseja adcionar:')
LISTA.append(ADD_ITEM)

## Salva a lista no arquivo
# Abre o arquivo para escrita ('w' -> write)
file = open("LISTA.txt", 'w')
# Itera a lista e escreve cada item no arquivo
for item in LISTA:
    # O str() converte o item em uma string
    # O '\n' no final é uma quebra de linha, pra cada item sair numa linha
    file.write(str(item) + '\n')
# Fecha o arquivo
file.close()

METHOD 1++

It is possible to use some Python features to dry this code, I commented what changed:

import os

LISTA = []

## Carrega a lista do arquivo
# Abre e fecha o arquivo (se ele já existe)
if os.path.exists("LISTA.txt"):
    with open("LISTA.txt", 'r') as file:
        # O resultado dessa função já é a lista que a gente quer
        # Deixa o "\n" e não adiciona na hora de escrever
        LISTA = file.readlines()

## Seu código
ADD_ITEM = input('Digite algo que deseja adcionar:')
LISTA.append(ADD_ITEM+"\n") # adiciona o "\n" só nos itens novos

## Salva a lista no arquivo
# Abre e fecha o arquivo
with open("LISTA.txt", 'w') as file:
    file.writelines(LISTA)

METHOD 2

Now, if you want to store more complex things than a list, this process starts to get too painful. So for this there is the module pickle, python native. This module takes variables and saves them in a "pickle", a binary file that can be opened later and recover the entire data structure, without worrying about doing this translation in hand.

I made an example using the pickle, well commented also:

import os
import pickle

LISTA = []

## Carrega a lista do arquivo
# Abre e fecha o picles (se ele já existe)
if os.path.exists("LISTA"):
    # Abre o arquivo em modo de leitura binária 'rb'
    with open("LISTA", 'rb') as file:
        LISTA = pickle.load(file)

## Seu código
ADD_ITEM = input('Digite algo que deseja adcionar:')
LISTA.append(ADD_ITEM)

## Salva a lista no picles
# Abre o arquivo em modo de escrita binária 'wb'
with open("LISTA", 'wb') as file:
    pickle.dump(LISTA, file)

## Não é possível ler o picles no editor de texto,
## então imprimo os valores aqui pra ver
print(LISTA)

Answer 2

It depends on the purpose of your application.

It can be Serialization in a file . txt if it is only text or in . xlsx and similar, if it is to organize the data in a spreadsheet. If you choose to use a BD, you have Sqlite which is more basic and saves records locally.

Regardless of choice, they are good options to practice and learn, if you are starting on programming.