How to keep string in list item after program ends - python

Question

In my program, I have an input function which adds a string to a list with multiple other values. Is there a way to keep the input in the list as an item after the program has ended?

For example:

list = ['a', 'b', 'c']

addToList = input('Type string to add to list: ')

list.append(addToList)

If I added the string 'd' through the variable 'addToList', how could I make it so the 'd' would be an item in the list next time I ran the program

Would look like this:

list = ['a', 'b', 'c', 'd']

addToList = input('Type string to add to list: ')

list.append(addToList)

Answer 1

Write the list on a file, you can do that in this way:

myFile = open('test.txt', 'w')
for item in myList:
    print>>myFile, item

Answer 2

You could follow tombam95's suggestion and write it out as a string, or a JSON object, then read from it when you start up the program again.

>>> file_ = open("test.json", "w")
>>> import json
>>> file_.write(json.dumps(["hi", "bye"]))
>>> file_.close()
>>> newf = open("test.json", "r")
>>> li = json.loads(newf.readline())
>>> li
[u'hi', u'bye']
>>> 

You could also shelve the variable as well, and you can read more about shelving here in the Python documentation.

Answer 3

Using the shelve module:

import shelve

db = shelve.open('mydata')  #=> creates file mydata.db
db['letters'] = ['a', 'b', 'c']
db.close()

#Time passes...

db = shelve.open('mydata')
print(db['letters'])

---

['a', 'b', 'c']

---

temp = db['letters']
temp.append('d')
db['letters'] = temp
db.close()

#Time passes...

db = shelve.open('mydata')
print(db['letters'])

---

['a', 'b', 'c', 'd']

Answer 4

You can use pickle to dump the object straight to file, that can then be read straight back into a new list object next time you start the program.

This example will create the file if it doesn't exist. (The file in the example below will be created in your working directory, unless the path is fully qualified)

import pickle

# Try and open the storage file
try:
    with open('storage_file', 'r') as f:
        my_list = pickle.load(f)

except (IOError, ValueError, EOFError):
    # File did not exist (IOError), or it was an invalid format (ValueError, EOFError)
    my_list = ['a', 'b', 'c']

addToList = input('Type string to add to list: ')
my_list.append(addToList)

print('List is currently: {}'.format(my_list))

# List is now updated, so write it back
with open('storage_file', 'w') as f:
    my_list = pickle.dump(my_list, f)

As a sidenote, don't use the word list as a variable, as it hides the list() function from your scope.