my function keeps checking the same index instead of checking the other index

Question

def capital_indexes(word):
    letters = []

    capital_letters = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z']

    index_letters = []

    # append letters in the word to a list
    for letter in word:
        letters.append(letter)

    # go through the letters in the list letters
    for i in letters:
        # checks if the indexes in the list match with the indexes in the list 'capital_leters'
        if i in capital_letters:
            index_letters.append(word.index(i))

    return index_letters


word_capital = capital_indexes('TEsT')
# this should return (0, 1, 3) but it keeps returning (0, 1, 0)

print(word_capital)

Answer 1

.index returns the first occurrence of a letter, use enumerate and .isupper:

def capital_indexes(word):
    return [i for i,l in enumerate(word) if l.isupper()]

Answer 2

Your code is highly inefficient, for instance the conversion to list is useless (you can iterate over a string), then looping through all capital letters is also inefficient (rather use a set). Finally, your main error resides in the fact that word.index(i) will always return the position of the first match (thus the 0 in place of 3).

Here is an alternative solution:

def capital_indexes(word):
    # general case for any given set of characters
    from string import ascii_uppercase
    letters = set(ascii_uppercase)
    return [i for i,c in enumerate(word) if c in letters]
    # case for uppercase only
    # return [i for i,c in enumerate(word) if c.isupper()]
        
capital_indexes('TEsT')
# [0, 1, 3]

Answer 3

This is because T is at index 0 and index 3, so index 0 is returned twice.

Try:

import string

result = [i for i, char in enumerate(word) if char in string.ascii_uppercase]

In your example:

>>> word = "TEsT"
>>> [i for i, char in enumerate(word) if char in string.ascii_uppercase]

[0, 1, 3]