将用户输入添加到列表中，如果输入存在于列表中，则将其删除；如果输入不存在，则将其追加

Question

So I want to ask a user to enter a letter for a pre-made list. If that letter already exists in that list , I want to have that letter deleted , if it does not exists in the list , I want it appended to the list. This is the code I'm using right now :

list1= ['a','b','c','d','e']
letter=input("please input a letter ")
for letter in list1:
    if letter in list1:
         del list1[letter]
         print(list1)
    else:
         print(list1.append(letter)

It gives the type-error that list indices must be integers not string. How do I go about this ?

Answer 1

You will need to pop the letter at the index. Also there is no need for the for loop. Edited answer to incorporate @lukasz comment.

list1= ['a','b','c','d','e']
letter=input("please input a letter ")
if letter in list1:
    list1.remove(letter)
else:
    print(list1.append(letter))

Answer 2

Pretty simple it is. Remove the value if it exists in the list, append if not.

list1= ['a','b','c','d','e']
letter=raw_input("please input a letter ")
list1.remove(letter) if letter in list1 else list1.append(letter)

Answer 3

If the letter is in list1 , you can use remove to delete it, and append can be used to add the new letter to the end of the list. The following script lets you see it working:

list1 = ['a','b','c','d','e']

while True:
    print('Current list:', list1)
    letter = input("Please input a letter: ")

    if letter in list1:
        list1.remove(letter)
    else:
        list1.append(letter)

For example:

Current list: ['a', 'b', 'c', 'd', 'e']
Please input a letter: f
Current list: ['a', 'b', 'c', 'd', 'e', 'f']
Please input a letter: b
Current list: ['a', 'c', 'd', 'e', 'f']
Please input a letter: a
Current list: ['c', 'd', 'e', 'f']