# Python | Convert list of numerical string to list of Integers

Many times, the data we handle might not be in the desired form for any application and has to go through the stage of preprocessing. One such kind of form can be a number in form of string that too as a list in list and we need to segregate it to be digit separated integers. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using list comprehension
This problem can be dealt with list comprehension, as a shorthand to generic loops that we would require to run to perform this particular task by iterating each list’s each character of string and converting to integer.

 `# Python3 code to demonstrate ` `# converting string list to integer list ` `# using list comprehension ` ` `  `# initializing list ` `test_list ``=` `[[``'24'``], [``'45'``], [``'78'``], [``'40'``]] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using list comprehension ` `# converting string list to integer list ` `res ``=` `[[``int``(i) ``for` `i ``in` `sub] ``for` `i ``in` `test_list ``for` `sub ``in` `i] ` ` `  `# print result ` `print``(``"The list after conversion : "` `+` `str``(res)) `

Output :

```The original list : [['24'], ['45'], ['78'], ['40']]
The list after conversion : [[2, 4], [4, 5], [7, 8], [4, 0]]
```

Method #2 : Using` map()` + list comprehension
The task performed in the above function can also be reduced to include the map function which bind the conversion to integer to a function and rest of task is performed by the list comprehension function itself.

 `# Python3 code to demonstrate ` `# converting string list to integer list ` `# using list comprehension + map() ` ` `  `# initializing list ` `test_list ``=` `[[``'24'``], [``'45'``], [``'78'``], [``'40'``]] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using list comprehension + map() ` `# converting string list to integer list ` `res ``=` `[``list``(``map``(``int``, ``list``(sub[``0``]))) ``for` `sub ``in` `test_list ``if` `sub ] ` ` `  `# print result ` `print``(``"The list after conversion : "` `+` `str``(res)) `

Output :

```The original list : [['24'], ['45'], ['78'], ['40']]
The list after conversion : [[2, 4], [4, 5], [7, 8], [4, 0]]
```

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