All elements aren't appearing when iterating through a loop

Question

My school assignment requires me to read a list from the user and then remove all odd elements from it. The loop I'm using to check for odd numbers doesn't even iterate through all the list elements.

ans=1
lst=[]
while ans!=0:
    no=int(input('Enter value for list or press 0 to exit:'))
    if no!=0:
        lst.append(no)
    else:
        break

print('\nYour list is:',lst)

       
for i in lst:     # loop to check for odd nos
    print('i is', i)
    if i%2==1:
        lst.remove(i)

print('List after removing odd elements:',lst)

In the second loop, I added the print statement to check the inconsistent output and here are the results: Output

Some of the list elements are skipped(?) when iterating and so they aren't removed which is giving me the incorrect output. Why could this be happening?

Does this answer your question? [How to remove items from a list while iterating?](https://stackoverflow.com/questions/1207406/how-to-remove-items-from-a-list-while-iterating) — JeffUK, Dec 03 '20 at 20:58
If you remove elements from the list while you're also iterating over that list, you will get interesting results. This question has some good answers that explain it a bit better https://stackoverflow.com/questions/6260089/strange-result-when-removing-item-from-a-list-while-iterating-over-it — JeffUK, Dec 03 '20 at 20:59

score 1 · Accepted Answer · answered Dec 03 '20 at 21:02

Creat a new list (to be allocated to lst) whitch select elements that respond to : elm%2 != 1

lst = [i for i in lst if i%2 != 1] #There will be no prints

With prints:

new_lst = []
for i in lst:
    print("i is ", i)
    if i%2 != 1:
       new_lst.append(i)
lst = new_lst

Can be also :

lst = list(filter(
    lambda x:( x % 2 ! = 1), #Each elements of lst is passed to this func
    lst                      #is the output of func is True (not 0) => add to list
))

score 0 · Answer 2 · answered Dec 03 '20 at 21:17

First, you read only to numbers. Second, since we know for sure that we have a number, we do not need to add the number if it is not even. Read user inputs until they enter -1

    list_even = []
    while True:
        try:
            digit = int(input('Enter value digit: '))
            if digit == -1: break
            elif digit % 2 == 0:
                list_even.append(digit)
        except ValueError:
            print('error is not digit')
            pass
    print('evens: ', list_even)

All elements aren't appearing when iterating through a loop

2 Answers2