# Converting List of String to Integer

Gary Herron gherron at islandtraining.com
Mon Jul 21 22:44:38 CEST 2008

```Samir wrote:
> On Jul 21, 3:20 pm, Gary Herron <gher... at islandtraining.com> wrote:
>
>> Samir wrote:
>>
>>> Hi Everyone,
>>>
>>> I am relatively new to Python so please forgive me for what seems like
>>> a basic question.
>>>
>>> Assume that I have a list, a, composed of nested lists with string
>>> representations of integers, such that
>>>
>>> a = [['1', '2'], ['3'], ['4', '5', '6'], ['7', '8', '9', '0']]
>>>
>>> I would like to convert this to a similar list, b, where the values
>>> are represented by integers, such as
>>>
>>> b = [[1, 2], [3], [4, 5, 6], [7, 8, 9, 0]]
>>>
>>> I have unsuccessfully tried the following code:
>>>
>>> n = []
>>> for k in a:
>>>     n.append([int(v) for v in k])
>>> print n
>>>
>>> Does anyone know what I am doing wrong?
>>>
>>>
>>> Samir
>>> --
>>> http://mail.python.org/mailman/listinfo/python-list
>>>
>> You didn't tell us how it failed for you, so I can't guess what's wrong.
>>
>> However, your code works for me:
>>
>>  >>> a = [['1', '2'], ['3'], ['4', '5', '6'], ['7', '8', '9', '0']]
>>  >>> n = []
>>  >>> for k in a:
>> ...    n.append([int(v) for v in k])
>> ...
>>  >>> print n
>> [[1, 2], [3], [4, 5, 6], [7, 8, 9, 0]]
>>
>> (Although you seem to have confused variables b and n.)
>>
>> Gary Herron- Hide quoted text -
>>
>> - Show quoted text -
>>
>
> Hi Gary,
>
> Thanks for your quick response (and sorry about mixing up b and n).
> For some reason, the logic I posted seems to work ok while I'm using
> the Python shell, but when used in my code, the program just hangs.
> It never outputs the results.  Below is the code in its entirety.  Is
> there a problem with my indendentation?
>
>
Aha.  There's the problem, right there in the first line.

> a = n = []
>

This sets a and n to the *same* empty list.    This line creates one
empty list and binds both n and a to that list.  Note carefully,  there
is only one empty list here, but it can be accessed under two names

for k in a:

runs through that list, and

n.append(...)

append to the end of the same list.  Thus the loop never get to the end of the (continually growing) list.

Solve it by creating two different empty lists:

a = []
n = []

Gary Herron

> t = """
> 1 2
> 3
> 4 5 6
> 7 8 9 0
> """
>
> d = t.split("\n")
>
> for x in range(1,len(d)-1):
>     a.append(d[x].split(" "))
> print a
>
> for k in a:
>     n.append([int(v) for v in k])
>
> print n
>
> Thanks again.
>
> Samir
> --
> http://mail.python.org/mailman/listinfo/python-list
>

```