TypeError: list indices must be integers

I'm trying to insert an item from one list to another and using an item from a list of numbers for the index but I'm getting this error even though I'm using integers for index numbers

and the other thing is that the same item is accepted as an index in the line just before the error

I even tried putting a number there just to test it but it gave me the same error

here's the code:

FoundLetters = ['p', 'l', '-', 'i', 'n']
MissingLetters = []
AllLetters = ['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']

def MissingCount():
    for j in range(len(FoundLetters)):
        if FoundLetters[j] == '-':

def iterate():
    for i in range(len(AllLetters)):
        for i in AllLetters:
            FoundLetters.insert(MissingLetters[0], AllLetters[i])


and this was the exact error:

Traceback (most recent call last):
File "main.py", line 26, in <module>
File "main.py", line 22, in iterate
FoundLetters.insert(MissingLetters[0], AllLetters[i])
TypeError: list indices must be integers or slices, not str

** Process exited - Return Code: 1 **
Press Enter to exit terminal

2 answers

  • answered 2022-05-06 16:38 Moritz Schaller

    the problem with your code is that you are using i twice in the iterate function. So you are overwriting the first i. Therefore you are looping through AlLLetters and you try to index AllLeters with strings like "a". Try to change the second loop

  • answered 2022-05-06 17:16 Samwise

    I'd suggest using itertools.product to generate all the possible replacement combinations:

    import itertools
    import string
    found_letters = "pl-in"
    missing_indices = [i for i, c in enumerate(found_letters) if c == "-"]
    possible_words = (''.join(
        r[i] if i in r else c
        for i, c in enumerate(found_letters)
    ) for r in (
        dict(zip(missing_indices, p))
        for p in itertools.product(
    print(list(possible_words))  # ['plain', 'plbin', ...]

    Using repeat with the number of missing letters will allow this to work regardless of the number of missing letters. In the above code, p is a product ('a', 'b', ...) and r is the replacement map for a given product ({2: 'a'}, {2: 'b'}, ...). When there are multiple -s in found_letters, each p will have that many letters ('aa', 'ab', ...) and r will map the location of each - to the letter that should replace it ({2: 'a', 4: 'a'}, {2: 'a', 4: 'b'}, ...).

    Note that the sequence of possible_words will get very large very quick if you have a lot of missing letters because it's exponential! Although it's convenient to turn it into a list when you want to print the whole thing, you may want to leave it in generator form so you can filter it through the English dictionary and drop all the nonsense words as you see them.

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