Convert List of Numerical String to List of Integers in Python

For data manipulation using python, we may come across scenario where we have strings containing numbers in a list. To be able to make calculations, we will need to change the strings into numbers. In this article we will see the ways to change the strings into numbers inside a list.

With int

The int function can be applied to the string elements of a list converting them to integers . We have to carefully design the for loops to go through each element and get the result even if there are multiple strings inside a single element.

Example

 Live Demo

listA = [['29','12'], ['25'], ['70']]
# Given lists
print("Given list A: ", listA)
# Use int
res = [[int(n) for n in element] for i in listA for element in i]
# Result
print("The numeric lists: ",res)

Output

Running the above code gives us the following result −

Given list A: [['29', '12'], ['25'], ['70']]
The numeric lists: [[2, 9], [1, 2], [2, 5], [7, 0]]

With map

We can also use the map function which will apply a given function again and again to each parameter that is supplied to this function. We create a for loop which fetches the elements form each of the inner lists. This approach does not work if the inner lists have multiple elements inside them.

Example

 Live Demo

listA = [['29'], ['25'], ['70']]
# Given lists
print("Given list A: ", listA)
# Use map
res = [list(map(int, list(elem[0]))) for elem in listA if elem ]
# Result
print("The numeric lists: ",res)

Output

Running the above code gives us the following result −

Given list A: [['29'], ['25'], ['70']]
The numeric lists: [[2, 9], [2, 5], [7, 0]]