convert a list of strings list into integers

Question

could you help me please? I use Python 3.x and would convert this variable ex into an integers list.

ex = [['2003', '12', '27', '7', '8646'],
      ['2003', '12', '28', '7', '7645'],
      ['2003', '12', '29', '2', '12823'],
      ['2003', '12', '30', '2', '14438'],
      ['2003', '12', '31', '3', '12374']]

I tried with this function but it doesn't work properly:

liste = []

def function_int(x):
    for i in x:
        liste.append(int[i])
    return liste

Thanks you for your support!

`liste` shouldn't be global for starters. Then are you aware that your input is a list of lists? not just a list? what is your expected result? — Jean-François Fabre, Oct 26 '17 at 20:52

score 3 · Answer 1 · answered Oct 26 '17 at 20:52

You're actually halfway there. You need a nested loop if you want to tackle nested lists.

Something like this.

def function_int(ex):
    liste = []
    for i in x:
        liste.append([])
        for j in i:
        liste[-1].append(int(i))

    return liste

At each outer iteration, we append the next inner list to our outer list. At each inner iteration, append the converted integer value to the most recently appended inner list.

Also note that int is a function, you call it with parenthesis, not square braces.

Alternatively, you could do this with a list comprehension.

liste = [[int(y) for y in x] for x in ex]

Which is much more concise with minimal loss in readability.

Another possibility is the possiblity of ValueErrors arising during conversion. You could take care of that only if you're working with the nested loop code. You'd use try-except handlers to do it.

try:
    liste[-1].append(int(i))
except ValueError:
    pass

@coldspeed, Thank you a lot. This one print what a expected: liste = [[int(y) for y in x] for x in ex] — Josh Bagwel, Oct 26 '17 at 21:16
I'm new here and don't yet know how to use the site. How can I vote? thanks. — Josh Bagwel, Oct 26 '17 at 21:32
@JoshBagwel Why did you unmark my answer? Please stick to a single answer _unless_ there's something wrong with it. You can't accept more than one answer. — cs95, Oct 29 '17 at 08:38

score 1 · Answer 2 · answered Oct 26 '17 at 21:08

1

Along with the other answers, here is another approach that you can use:

integer_x = [list(map(int, each)) for each in x]
print(integer_x)

answered Oct 26 '17 at 21:08

Deepayan Ghosh

185
2
9

.Thank you very much for your help. – Josh Bagwel Oct 26 '17 at 21:23
@JoshBagwel No problem. Always happy to help. If you find it helpful, don't forget to vote. – Deepayan Ghosh Oct 26 '17 at 21:34

score 1 · Answer 3 · answered Oct 26 '17 at 21:11

1

take a look at the ast module

you can do this:

import ast
liste = []  
for l in ex:
   for i in range(len(l)):
      l[i] = ast.literal_eval(l[i])
   liste.append(l)

answered Oct 26 '17 at 21:11

Simon Mengong

2,625
10
22

Why would you use such a heavy module for a simple integer conversion? – cs95 Oct 26 '17 at 21:12
It's a built-in module and it is generaly used for those kind of things – Simon Mengong Oct 26 '17 at 21:16
If you were to ask someone to pick between `int` and `ast` as to which function is used to parse a string representation of an integer, you'd almost always get `int` as the response. – cs95 Oct 26 '17 at 21:18
of course ! It is not the subject but imagine that **ex** was a string and you want to convert it to a list of list of integers, that's the work of **ast** – Simon Mengong Oct 26 '17 at 21:21
You're right there. If the entire input was a string. ;-) – cs95 Oct 26 '17 at 21:23
@JoshBagwel you are werlcome – Simon Mengong Oct 27 '17 at 13:23

ragardner · Accepted Answer · 2017-10-27T11:36:52.423

this is the fastest most memory efficient way of doing it in my opinion, note: it will overwrite ex if you want a new list then change ex[:] = to liste = or whatever you want to call your variable

try:
    #check out this module for faster string checking
    from fastnumbers import *
except:
    pass

ex = [['2003', '12', '27', '7', '8646'],
      ['2003', '12', '28', '7', '7645'],
      ['2003', '12', '29', '2', '12823'],
      ['2003', '12', '30', '2', '14438'],
      ['2003', '12', '31', '3', '12374']]

ex[:] = [[int(e) if e.isdigit() else e for e in sl] for sl in ex]

results:

for sublist in ex:
    print (sublist)

[2003, 12, 27, 7, 8646]
[2003, 12, 28, 7, 7645]
[2003, 12, 29, 2, 12823]
[2003, 12, 30, 2, 14438]
[2003, 12, 31, 3, 12374]

To explain slice notation, especially being used on the left of = please see this question: How assignment works with python list slice

Thank you @new_to_code for your help. Your solution is an other way. — Josh Bagwel, Oct 29 '17 at 00:03

convert a list of strings list into integers

4 Answers4