How do I save a list to file using python?

Question

I was wondering how I can save a list entered by the user. I was wondering how to save that to a file. When I run the program it says that I have to use a string to write to it. So, is there a way to assign a list to a file, or even better every time the program is run it automatically updates the list on the file? That would be great the file would ideally be a .txt.

stuffToDo = "Stuff To Do.txt"
WRITE = "a"
dayToDaylist = []
show = input("would you like to view the list yes or no")
if show == "yes":
    print(dayToDaylist)

add = input("would you like to add anything to the list yes or no")
if add == "yes":
    amount=int(input("how much stuff would you like to add"))
    for number in range (amount):
        stuff=input("what item would you like to add 1 at a time")
        dayToDaylist.append(stuff)
remove = input("would you like to remove anything to the list yes or no")
    if add == "yes":        
    amountRemoved=int(input("how much stuff would you like to remove"))
    for numberremoved in range (amountRemoved):
        stuffremoved=input("what item would you like to add 1 at a time")
        dayToDaylist.remove(stuffremoved);
print(dayToDaylist)

file = open(stuffToDo,mode = WRITE)
file.write(dayToDaylist)
file.close()

By the way, it's generally MORE readable to "hard-code" the mode parameter to open(), not less. Using that pseudo-constant is just confusing. Also, you don't need to give it as a keyword argument; you can just call it as `open("filename", "a")` — Schilcote, Nov 15 '14 at 23:19

Padraic Cunningham · Answer 1 · 2014-11-15T23:40:28.130

5

You can pickle the list:

import pickle

with open(my_file, 'wb') as f:
    pickle.dump(dayToDaylist, f)

To load the list from the file:

with open(my_file, 'rb') as f:
    dayToDaylist = pickle.load( f)

If you want to check if you have already pickled to file:

import pickle
import os
if os.path.isfile("my_file.txt"): # if file exists we have already pickled a list
    with open("my_file.txt", 'rb') as f:
        dayToDaylist = pickle.load(f)
else:
    dayToDaylist  = []

Then at the end of your code pickle the list for the first time or else update:

with open("my_file.txt", 'wb') as f:
    pickle.dump(l, f)

If you want to see the contents of the list inside the file:

import ast
import os
if os.path.isfile("my_file.txt"):
    with open("my_file.txt", 'r') as f:
        dayToDaylist = ast.literal_eval(f.read())
        print(dayToDaylist)

with open("my_file.txt", 'w') as f:
    f.write(str(l))

edited Nov 15 '14 at 23:40

answered Nov 15 '14 at 22:56

Padraic Cunningham

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sorry mate i am really new to this i have pickled the list but how can i get that to be read if i open the file? – cizwiz Nov 15 '14 at 23:26
have you used the `pickle.load` example? – Padraic Cunningham Nov 15 '14 at 23:28
yes and when i open the file it still has the starnge charters around the list – cizwiz Nov 15 '14 at 23:34
do you want to reuse the list or look at it inside a file? Your question seemed to want to just reuse the list – Padraic Cunningham Nov 15 '14 at 23:36
ok I will add another way – Padraic Cunningham Nov 15 '14 at 23:38

score 0 · Answer 2 · edited May 23 '17 at 12:23

0

for item in list: file.write(item)

You should check out this post for more info: Writing a list to a file with Python

edited May 23 '17 at 12:23

Community

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answered Nov 15 '14 at 22:54

Prasad Shinde

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score 0 · Answer 3 · answered Nov 15 '14 at 23:17

Padraic's answer will work, and is a great general solution to the problem of storing the state of a Python object on disk, but in this specific case Pickle is a bit overkill, not to mention the fact that you might want this file to be human-readable.

In that case, you may want to dump it to disk like such (this is from memory, so there may be syntax errors):

with open("list.txt","wt") as file:
    for thestring in mylist:
        print(thestring, file=file)

This will give you a file with your strings each on a separate line, just like if you printed them to the screen.

The "with" statement just makes sure the file is closed appropriately when you're done with it. The file keyword param to print() just makes the print statement sort of "pretend" that the object you gave it is sys.stdout; this works with a variety of things, such as in this case file handles.

Now, if you want to read it back in, you might do something like this:

with open("list.txt","rt") as file:
    #This grabs the entire file as a string
    filestr=file.read()
mylist=filestr.split("\n")

That'll give you back your original list. str.split chops up the string it's being called on so that you get a list of sub-strings of the original, splitting it every time it sees the character you pass in as a parameter.

How do I save a list to file using python?

3 Answers3