Definition: In this task, you are given an input list A. You need to convert all the alphabets in the list with a number representing their position in the English alphabet. E.g., replace A by 1, B by 2, a by 1, b by 2, and so on.
Input: ['5515', 't', 'T', '4305', 'w', 'O', 'S', '1587', 's', '1539', '4021', '6697', '9235', 'e', 'D', 'R', 's', 'C', '7753']

5515, 20, 20, 4305, 23, 15, 19, 1587, 19, 1539, 4021, 6697, 9235, 5, 4, 18, 19, 3, 7753