Converting a list of str into list of int python

Question

I have the following input:

669  866  147
 15  881  210
662   15   70

Using .split('\n') on it, I am able to get a list of 3 strings. Then I would like to break each string to a list of strings and then convert those to int. The code I'm trying to use for this so far is

for tr in numbers:
    tr = tr.split()
    tr = list(map(int, tr))

However, after the for loop closes nothing happened to the original list, so if I run this command print(type(numbers[0])) it returns <class 'str'>.

I am guessing this is due to the operation happening inside the loop so outside it nothing changed, so how would I go about making it so the original list updates too?

Anshul Goyal · Accepted Answer · 2016-12-08 13:15:09Z

2

You will have to explicitly set the lists back to the numbers list, right now, you are only manipulating a variable tr with re-assignment, so the original list doesn't get affected. Try this instead

>>> numbers = ["669  866  147", " 15  881  210", "662   15   70"]
>>> for idx, tr in enumerate(numbers):
...     tr = tr.split()
...     numbers[idx] = list(map(int, tr))
... 
>>> numbers
[[669, 866, 147], [15, 881, 210], [662, 15, 70]]

answered Dec 8, 2016 at 13:15

Anshul Goyal

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4 Comments

rain-m Over a year ago

Works perfectly, thank you for explaining as well I perfectly understand now, much appreciated!

Anshul Goyal Over a year ago

@AngelosH Happy to help, don't forget to accept and upvote the answer :)

Ben Hoyt Over a year ago

Generally more idiomatic to use a list comp: numbers[idx] = [int(n) for n in tr.split()]

Anshul Goyal Over a year ago

@BenHoyt Agreed, though I just wanted to do minimal number of changes so its easier to understand.

Leo · Accepted Answer · 2016-12-08 13:27:16Z

2

A one-liner for this could be like this:

In [6]: numbers = "669 866 147\n15 881 210\n662 15 70"

In [7]: [[int(y) for y in x.split()] for x in numbers.split('\n')]
Out[7]: [[669, 866, 147], [15, 881, 210], [662, 15, 70]]

You can assign In [7] directly back to numbers, or into a separate new variable.

answered Dec 8, 2016 at 13:27

Leo

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1 Comment

rain-m Over a year ago

Yep this works very nicely too, thanks for the one-liner!

Ari Gold · Accepted Answer · 2016-12-08 13:25:22Z

0

import re
numbers = ["669  866 ASSASSA 147", " 15  881  210", "662   15   70"]
numbers = [[int(_str) for _str in re.findall(r"\d+", o)] for o in numbers]
print numbers
# [[669, 866, 147], [15, 881, 210], [662, 15, 70]]

answered Dec 8, 2016 at 13:25

Ari Gold

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Comments

Tyson · Accepted Answer · 2016-12-08 14:27:44Z

0

The Pythonic way would be to use a list comprehension - avoiding enumeration/indexing, mutation and a new variable in the scope:

>>> numbers = ["669  866  147", " 15  881  210", "662   15   70"]
>>> numbers = [map(int, tr.split()) for tr in numbers]
>>> numbers
[[669, 866, 147], [15, 881, 210], [662, 15, 70]]

Some people avoid the map builtin, in which case you could substitute the second line with this:

numbers = [[int(n) for n in tr.split()] for tr in numbers]

answered Dec 8, 2016 at 14:27

Tyson

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