Need to get the 0 index of the first list and the 0 index of the inner list to be able to use split on '1 A'.
>>> my_list = [['1 A'], ['2 B']] >>> a, b = my_list[0][0].split() >>> my_list[0][0] = '{} {}'.format(int(a)+10, b) >>> my_list [['11 A'], ['2 B']] >>>