Python saving list changes

Question

list = []
while True:
    list.append(input())
    print(list)

this allows me to add whatever I want to this list. However, Is there a way that I can keep the changes to the list so that when I run the program later all of the things I previously wrote will be on the list?

EDIT: If it matters, I use PyCharm for coding and running my progams

Consider saving the list to a text file or wherever. Then you can just load the list from the source and append new records. — Eduard, Jul 08 '16 at 10:56
You'd need to dump the list to some persistent storage (e.g., a file, a database table) and read it when the program starts. — Mureinik, Jul 08 '16 at 10:56
This may help: [Python pickle/unpickle a list to/from a file](http://stackoverflow.com/questions/18229082/python-pickle-unpickle-a-list-to-from-a-file) — Moses Koledoye, Jul 08 '16 at 10:57

score 1 · Accepted Answer · answered Jul 08 '16 at 11:02

1

You can use json here.

import json
try:
    list = json.load(open("database.json"))
except:
    list = []
while True:
    try:
        list.append(input())
        print(list)
    except KeyboardInterrupt:
        json.dump(list, open('database.json', 'w'))

This stores the content in a file called database.json, you can end the program with CTRL+C

answered Jul 08 '16 at 11:02

Siddharth Gupta

1,573
9
24

Gupta I tried that, but when I ran the program a second time the list contents had been removed – Adde21_30 Jul 08 '16 at 11:25
You were closing the program using? – Siddharth Gupta Jul 08 '16 at 11:27
PyCharm, and I want to be able to close it in PyCharm too – Adde21_30 Jul 08 '16 at 11:30
Also I tried it in python and closed it with CTRL + C and that didn't work either – Adde21_30 Jul 08 '16 at 11:39
After `json.dump(...` in the except clause do `exit()` – joel goldstick Jul 08 '16 at 12:00
Also, not good to shadow `list`. maybe change to `my_list` since `list` is a type – joel goldstick Jul 08 '16 at 12:08

score 0 · Answer 2 · answered Jul 08 '16 at 11:02

You would need a persistence layer i.e a file system, database, pickle, shelve etc. where you can store the data present in list once the program has terminated. When you re-run your program, make sure it loads from the same persistence store, without initializing it to [] and that is how you would be able to store the elements appended to the list.

Python provides many alternatives as described here

score 0 · Answer 3 · answered Jul 08 '16 at 11:05

You need to save the list somewhere first and then load it at the start of the program. Since it's just a simple list we can just use python pickle to save it to disk like this:

import pickle

try:
    with open('list.p', 'rb') as f:
        list = pickle.load(f)
except:
    list = []
while True:
    try:
        list.append(input())
        print(list)
    except KeyboardInterrupt:
        with open('list.p', 'wb') as f:
            pickle.dump(list, f)

Python saving list changes

3 Answers3