Write and read a list from file

If you don't need it to be human-readable/editable, the easiest solution is to just use pickle.

To write:

with open(the_filename, 'wb') as f:    pickle.dump(my_list, f)

To read:

with open(the_filename, 'rb') as f:    my_list = pickle.load(f)

If you do need them to be human-readable, we need more information.

If my_list is guaranteed to be a list of strings with no embedded newlines, just write them one per line:

with open(the_filename, 'w') as f:    for s in my_list:        f.write(s + '\n')with open(the_filename, 'r') as f:    my_list = [line.rstrip('\n') for line in f]

If they're Unicode strings rather than byte strings, you'll want to encode them. (Or, worse, if they're byte strings, but not necessarily in the same encoding as your system default.)

If they might have newlines, or non-printable characters, etc., you can use escaping or quoting. Python has a variety of different kinds of escaping built into the stdlib.

Let's use unicode-escape here to solve both of the above problems at once:

with open(the_filename, 'w') as f:    for s in my_list:        f.write((s + u'\n').encode('unicode-escape'))with open(the_filename, 'r') as f:    my_list = [line.decode('unicode-escape').rstrip(u'\n') for line in f]

You can also use the 3.x-style solution in 2.x, with either the codecs module or the io module:*

import iowith io.open(the_filename, 'w', encoding='unicode-escape') as f:    f.writelines(line + u'\n' for line in my_list)with open(the_filename, 'r') as f:    my_list = [line.rstrip(u'\n') for line in f]

_{* TOOWTDI, so which is the one obvious way? It depends… For the short version: if you need to work with Python versions before 2.6, use codecs; if not, use io.}

As long as your file has consistent formatting (i.e. line-breaks), this is easy with just basic file IO and string operations:

with open('my_file.txt', 'rU') as in_file:    data = in_file.read().split('\n')

That will store your data file as a list of items, one per line. To then put it into a file, you would do the opposite:

with open('new_file.txt', 'w') as out_file:    out_file.write('\n'.join(data)) # This will create a string with all of the items in data separated by new-line characters

Hopefully that fits what you're looking for.

Let's define a list first:

lst=[1,2,3]

You can directly write your list to a file:

f=open("filename.txt","w")f.write(str(lst))f.close()

To read your list from text file first you read the file and store in a variable:

f=open("filename.txt","r")lst=f.read()f.close()

The type of variable lst is of course string. You can convert this string into array using eval function.

lst=eval(lst)