Why is my Python code returning a list of characters instead of items?

Question

Question:

I'm trying to solve the following problem: given two arrays of strings list1 and list2, find the common strings with the least index sum.

A common string is a string that appeared in both list1 and list2. A common string with the least index sum is a common string such that if it appeared at list1[i] and list2[j] then i + j should be the minimum value among all the other common strings. I need to return all the common strings with the least index sum.

Here's the code that I've written so far:

class Solution:
    def findRestaurant(self, list1: List[str], list2: List[str]) -> List[str]:
        res = []
        smallest_n = float('inf')
        for i in range(len(list1)):
            if list1[i] in list2:
                res.append(list1[i])
        if len(res) == 0:
            return False
        if len(res) == 1:
            return res.pop()
        if len(res) > 1:
            for i in range(len(res)):
                n = list1.index(res[i]) + list2.index(res[i])
                if n < smallest_n:
                    smallest_n = n
            result = []
            for i in range(len(res)):
                n = list1.index(res[i]) + list2.index(res[i])
                if n == smallest_n:
                    result.append(res[i])
            return result

My issue is that the code is returning a list of characters instead of items. How can I modify my code so that it returns the expected list of items instead?

Any help would be greatly appreciated!

I tried to return a list of the least index sum string with each item being a word, but instead, I returned the (correct) result as a list of characters of the word.

I attempted to change the result.append(res[i]) to result.append(str(res[i]), but I got the same result.

Edit: an example of an input with unexpected results would be:

["Shogun","Tapioca Express","Burger King","KFC"]
["Piatti","The Grill at Torrey Pines","Hungry Hunter Steakhouse","Shogun"]
Output:
["S","h","o","g","u","n"]
Expected:
["Shogun"]```

Edit: thank you very much for all the help, the error was using .pop() to return the only value in the list rather than the list itself.

Answer 1

If you look at function definition

class Solution:
    def findRestaurant(self, list1: List[str], list2: List[str]) -> List[str]:

As you can see from the highlighted part the expected output is List of str

As @slothrop pointed out in the comment res.pop() which is the operation being performed on List of str if we look at pop function definition

 |  pop(self, index=-1, /)
 |      Remove and return item at index (default last).
 |      
 |      Raises IndexError if list is empty or index is out of range.

It return item if present, if index provided then remove item at index and return or if item not found raises error.

Since res is List as defined in first line of the function body which contains str item which is what gets returned in this case Shogan string.

To fix the issue you can just directly return res which is List only containing single item Shogan string and what is expected in return as per function definition

The output ["S","h","o","g","u","n"] which is printed by platform checker As @slothrop pointed is probably looping over the string or trying to convert it to list list('Shogan') and then compare with expected output