extract only numbers from list python code example

Example 1: how to extract numbers from a list in python

a = ['1 2 3', '4 5 6', 'invalid']
numbers = []
for item in a:
    for subitem in item.split():
        if(subitem.isdigit()):
            numbers.append(subitem)
print(numbers)

['1', '2', '3', '4', '5', '6']

Example 2: extract numbers from list of strings python using regex

new_list = [int(item) for sublist in a for item in sublist if item.isdigit()]