Why am I getting a IndexError: list index out of range error in the code below?

Question

I just want to remove the duplicates of the word passed but it's not working.

wordlist = ["a", "a", 'b', "b", "b", "c", "d", "e"]
new_list = wordlist
word = "a"

for i in range(len(wordlist)):
    if wordlist[i] == word:
        new_list.remove(word)

print(new_list)

new_list and wordlist are the same object in your case. id(new_list) equals with id(wordlist). Pay attention on mutability in python. — basckerwil, Feb 11 '21 at 14:51
If the order doesn't matter the easiest way is `new_list = list(set(wordlist))` — anishtain4, Feb 11 '21 at 15:16

score 1 · Answer 1 · answered Feb 11 '21 at 14:47

Because new_list and wordlist point to the same object. You should use new_list = wordlist.copy() to create the copy of the list.

wordlist = ["a", "a", 'b', "b", "b", "c", "d", "e"]
new_list = wordlist.copy()
word = "a"

for i in range(len(wordlist)):
    if wordlist[i] == word:
        new_list.remove(word)

print(new_list)

Note: It is not advisable to modify the containers while iterating over the same.

score 1 · Answer 2 · answered Feb 11 '21 at 14:55

This post explained well.

In order to make it work, you have to explicitly ask for a copy.

wordlist = ["a", "a", 'b', "b", "b", "c", "d", "e"]
new_list = list(wordlist)

word = "a"

for i in range(len(wordlist)):
    if wordlist[i] == word:
        new_list.remove(word)

print(new_list)

score 0 · Answer 3 · answered Feb 11 '21 at 14:47

Either make new_list a true shallow copy:

new_list = wordlist[:]

Otherwise, new_list is just another reference to the same list object and your initially created range reaches indeces that no longer exist after a couple of removals.

Or (better) build it from scratch:

new_list = [w for w in word_list if w != word]

Why am I getting a IndexError: list index out of range error in the code below?

3 Answers3