If I understood you well you wants to continue storing data in a list.
The code below will continue to ask for input and store in a list until you enter
the value True.
myList = 
tester = True
a = input('Enter Value: ')
if a == 'True':
tester = False
I generally prefer to use the 'a' option when opening a file, as it means that the stuff that has been inputted is added to the file, rather than overwriting all the other data that is in the file already. For example, if you are going to save the results of a quiz or a game, then appending would be much more efficient. The only time I would use the 'w' option would be if I were going to update the data in a file, if there is only one set of it
If you want to store data as native python list object inside a file you can use standard module Pickle. Storing programming language objects inside binary files called serialization, reverse process called de-serialization. Example:
some_list = [1,2,3]
#store data inside "some_file.p"
pickle.dump( some_list, open( "some_file.p", "wb" ) )
#load data from "some_file.p"
other_list= pickle.load( open( "save.p", "rb" ) )
#Do you mean something like that :
usr = input ("enter what you want to write :")
file = open("file.txt", "w")
#If yes thank you verry much
#if i did'nt understood explain me more