reading values from a text file and storing it into lists

Question

I have values in a text file which will be like this for example:

1,2,3,4
1,1,1,1
4,3,2,1
2,2,2,2
   ...etc

now i want to store each line into a list and thus, i have created a list of lists to store these values

numbers = [[]]

how would i go about storing these values into the list so that from the example aboe:

numbers[1] = [1,2,3,4]
          ... etc

so far i have this:

    with open(s) as f :
    for s in f:
        numbers = [l.split(',') for l in f.readline()]

but i am unsure if this is the correct way to do it, or if there is better way to do it

Thanks in advance for the help

Answer 1

You should cast your input as int. Also, you can do it as a one-liner:

with open('test.txt') as f:
    numbers = [[int(j) for j in i.split(',')] for i in f.read().split('\n')]

>>> print numbers
[[1,2,3,4],
 [1,1,1,1],
 [4,3,2,1],
 [2,2,2,2]]

Answer 2

You can use the csv module with a list comprehension and/or map :

import csv
with open('text1.txt') as f:
    numbers = [map(int, row) for row in csv.reader(f)]

>>> numbers
[[1, 2, 3, 4], [1, 1, 1, 1], [4, 3, 2, 1], [2, 2, 2, 2]]

For Python 3 you'll have to add an extra list call around map or use a list comprehension(Will work in both Python 2 and 3):

numbers = [list(map(int, row)) for row in csv.reader(f)]
#or
numbers = [[int(x) for x in row] for row in csv.reader(f)]

---

Without importing any module you can do:

>>> with open('text1.txt') as f:
    numbers = [[int(x) for x in line.split(',')] for line in f]
...     
>>> numbers
[[1, 2, 3, 4], [1, 1, 1, 1], [4, 3, 2, 1], [2, 2, 2, 2]]

Here as you can see you need to iterate over the file object not file.readline , iteration over a file object returns one line at a time, and then we split that line and case its items to integers. ( file.readline() only returns one line, and in your code you were only iterating over that line, which is wrong.)

Answer 3

rows = []
with open("foo.txt") as f:
    rows = [l.split() for l in f]

Output

[['1,2,3,4'], ['1,1,1,1'], ['4,3,2,1'], ['2,2,2,2']]