Can't add the last element in the list in python

Question

def front_x(words):
list2 = []
for word in words:
    if word[0] == 'x':
        list2.append(word)
        words.remove(word)
words.sort()
list2.sort()

return list2 + words




def main():
    print(front_x(['bbb', 'ccc', 'axx', 'xzz', 'xaa']))




if __name__ == '__main__':
    main()

This is my code I'm trying to do this example:

Given a list of strings, return the count of the number of strings where the string length is 2 or more and the first and last chars of the string are the same. Note: python does not have a ++ operator, but += works.

and the output is like this : ['xzz', 'axx', 'bbb', 'ccc', 'xaa']

The problem is the last element on the list don't go to the new list I created. What should I do?

Please explain what you mean by "The problem is the last element on the list don't go to the new list I created" — CutePoison, Oct 20 '21 at 06:10
[re](https://docs.python.org/3/library/re.html) module may be useful here. — chickity china chinese chicken, Oct 20 '21 at 06:13
isn't this code work totally differnet from prblem statement? — sahasrara62, Oct 20 '21 at 06:18
Do not delete its elements during the iteration. You can modify `for word in words.copy()` as follows. — pppig, Oct 20 '21 at 06:25

score 2 · Answer 1 · answered Oct 20 '21 at 06:27

You shouldn't change the words when you are iterating through it, otherwise it'll lead to some bugs. You need iterate the copy of words to avoid changing it.
You remove the words when word[0] == 'x', which cause the loop end before you want.
You can use debug mode in IDE(such as VSCode, PyCharm) to run your code line by line to check what actually happened in runtime.

example code:

def front_x(words):
    list2 = []
    for word in words.copy():
        if word[0] == 'x':
            list2.append(word)
            words.remove(word)
    words.sort()
    list2.sort()

    return list2 + words

def main():
    print(front_x(['bbb', 'ccc', 'axx', 'xzz', 'xaa']))

main()

result:

['xaa', 'xzz', 'axx', 'bbb', 'ccc']

score 0 · Answer 2 · answered Oct 20 '21 at 06:27

This is because you are removing the element from the same list you are iterating . After removing an element from list , element position shift. When iteration pointer is on second last element list changes from ['bbb', 'ccc', 'axx', 'xzz', 'xaa'] to ['bbb', 'ccc', 'axx', 'xaa']. Thus iteration pointer now points to last element .

score -2 · Answer 3 · answered Oct 20 '21 at 06:22

In this problem the question wants you to use 2 different things:

len function
list indexing

`len`

len returns the size of a container. A container can be a str, list, tuple, etc.

To check if the length of the given string is equal or bigger then 2.

if len(word) >= 2:

indexing

Accessing the first element of a container (in your example a string) is easy. You can get the 0th element like:

word[0]

But you will need to get the last element of a container and your strings can change in length. So you must come with a method to get the last element of the container.

You, again, can use the len function. like:

last_char = word[len(word) - 1]

or you can use negative indexes.

last_char = word[-1]

Can't add the last element in the list in python

3 Answers3

example code:

result:

len

indexing

`len`