How to write a list to a text file in python?

Question

I am running through the learn python the hard way tutorials, and I was trying to make my own project that incorporates some of the basic concepts. We haven't covered loops yet, so as a forewarning, if you are going to include a loop in your answer, please do so under the assumption that I've never seen them before :)

this is my code, which works up until I try and write the list to the file. I get the error message that write expected a string. Is there any way to trick write into thinking that the list is a string?

from sys import argv
script, file1 = argv

def rewind(f):
    f.seek(0)

txt = open(file1, 'a+')
txt.write(raw_input("What would you like to add to the file?:\n"))
rewind(txt)
text = txt.read()
print text
def breakwords(f):
    split_words = f.split(' ')
    return split_words
brkwrds = breakwords(text)
print brkwrds
def sort_words(f):
    sorted_words = sorted(f)
    return sorted_words
sw = sort_words(brkwrds)

rewind(txt)
txt.truncate()
txt.write(sw)

Answer 1

You can join all the strings in the list with str.join :

my_list = ['a', 'few', 'words']
my_string = ' '.join(my_list)

Here, I'm joining all the string in my_list using a white space as the separator. The result is a string ( 'a few words' ) that can be written to a file.

Answer 2

You can use pickle to convert the object into a string and then string escape the pickled string so that the result is a single line (when stored in a file).

A python 2X approach is:

from sys import argv
script, file1 = argv
import pickle
def rewind(f):
    print(f.seek(0))
    f.seek(0)

txt = open(file1, 'a+')
txt.write(raw_input("What would you like to add to the file?:\n"))
rewind(txt)
text = txt.read()
print text
def breakwords(f):
    split_words = f.split(' ')
    return split_words
brkwrds = breakwords(text)
print brkwrds
def sort_words(f):
    sorted_words = sorted(f)
    return sorted_words
sw = sort_words(brkwrds)

rewind(txt)
txt.truncate()
txt.write(pickle.dumps(sw).encode("string-escape")+"\n")
txt.close()

To decode the pickled object from the file to get your list back. something like this

my_list_resurrected=pickle.loads(line_in_file.decode("string-escape"))