Converting a string into a list in Python

Question

I have a text document that contains a list of numbers and I want to convert it to a list. Right now I can only get the entire list in the 0th entry of the list, but I want each number to be an element of a list. Does anyone know of an easy way to do this in Python?

1000
2000
3000
4000

to

['1000','2000','3000','4000']

• Eric Wilson: Do you really want ['1000','2000','3000','4000']? Maybe [1000,2000,3000,4000] would be better?
• Omnifarious: Your question admits of too many possibilities. Does the text file only contain a list of numbers, or is that list in a larger context. Do you get to control how you read from the document or are you stuck with having read a string that contains a bunch of newline or whitespace separated numbers? Are the numbers in the list always separated by newlines, or are they sometimes separated by other whitespace? Do you really want a list of strings as your result, or would a list of integers be better?

Answer 1

To convert a Python string into a list use the str.split method:

>>> '1000 2000 3000 4000'.split()
['1000', '2000', '3000', '4000']

split has some options: look them up for advanced uses.

You can also read the file into a list with the readlines() method of a file object - it returns a list of lines. For example, to get a list of integers from that file, you can do:

lst = map(int, open('filename.txt').readlines())

---

P.S: See some other methods for doing the same in the comments. Some of those methods are nicer (more Pythonic) than mine

• SilentGhost: you're using str.split, not string.split, the latter is obsolete anyway.
• Mike Graham: File objects are iterable, so there is seldom a reason to use the readlines method. For example, you could get the same results as your last snippet with map(int, open('filename.txt')).
• Ruslan Spivak: List comprehension is usually faster than map built-in function plus if the file is big enough iteration over file will be faster and more memory efficient than readlines: lst = [int(line) for line in open('filename.txt')]
• Omnifarious: lst = [int(line) for line in open('filename.txt')] is much better (and more efficient) idiomatic Python for your second example. chuckle I should read the other comments before I post one.
• Paolo Moretti: This will not close the file. The correct way should be: with open('filename.txt') as f: lst = map(int, f.readlines())

Answer 2

 $ cat > t.txt
 1
 2
 3
 4
 ^D
 $ python
 Python 2.6.1 (r261:67515, Jul 7 2009, 23:51:51) 
 [GCC 4.2.1 (Apple Inc. build 5646)] on darwin
 Type "help", "copyright", "credits" or "license" for more information.
 >>> l = [l.strip() for l in open('t.txt')]
 >>> l
 ['1', '2', '3', '4']
 >>> 

Answer 3

>>> open("myfile.txt").readlines()
>>> lines = open("myfile.txt").readlines()
>>> lines
['1000\n', '2000\n', '3000\n', '4000\n']
>>> clean_lines = [x.strip() for x in lines]
>>> clean_lines
['1000', '2000', '3000', '4000']

Or, if you have a string already, use str.split:

>>> myfile
'1000\n2000\n3000\n4000\n'
>>> myfile.splitlines()
['1000', '2000', '3000', '4000', '']

You can remove the empty element with a list comprehension (or just a regular for loop)

>>> [x for x in myfile.splitlines() if x != ""]
['1000', '2000', '3000', '4000']

• Devin Jeanpierre: use s.splitlines(), not s.split("\n")

Answer 4

 with open('file.txt', 'rb') as f:
 data = f.read()
 lines = [s.strip() for s in data.split('\n') if s]

Answer 5

You can achieve this using the splitlines() method in python

data = """1000
2000
3000
4000"""
number_list = data.splitlines()

Answer 6

You might need to strip newlines.

# list of strings
[number for number in open("file.txt")]
# list of integers
[int(number) for number in open("file.txt")]

• Omnifarious: And, if the OP were to need to strip newlines, how would that code look?
• dbr: You can also just use the list builtin instead of a list comprehension - list(open("myfile.txt")) -> ['1000\n', '2000\n', '3000\n', '4000\n']
• dbr: @SilentGhost True, it makes it clearer what is happening, but list(open("myfile")) is the same as open("myfile").readlines() - by default iterating over a file with use the readlines method

Answer 7

If you already have a list that has been converted to a string by the str() method--like str(my_list)-- I have found that the easiest way to convert it back into a list is just to use eval(file_contents).