Replacing duplicate item in list through raw_input

Question

Completely new to Python so bear with me.

I created a list through raw_input:

itemList = []
num = int (raw_input("Enter a number: "))
for i in range (num):
    listStr = raw_input("Enter an item: ")
    itemList.append (listStr)

Now I have to check if any item already exists, and if it does ask for another raw_input to add to list. I'm completely stumped. It's not looping with this; it just prints a anyway.I also then have to append new item to original list. Stumped.

itemList = []
num = int (raw_input("Enter a number: "))
for i in range (num):
    listStr = raw_input("Enter an item: ")
    itemList.append (listStr)
for a in itemList:
    if a in itemList :
        a = raw_input("Enter another number: ")

Answer 1

You can use a while loop to keep asking for input until an item is entered that isn't already in the list. This could be improved, but it should get you started:

itemList = []
num = int (raw_input("Enter a number: "))

for i in range (num):

    while True:
        listStr = raw_input("Enter an item: ")
        if listStr in itemList:
            print('That item is already in the list')
        else:
            itemList.append(listStr)
            break

Slightly better version:

itemList = []
num = int(raw_input("Enter a number: "))

for i in range(num):

    listStr = raw_input("Enter an item: ")

    while listStr in itemList:
        print("That item already exists")
        listStr = raw_input("Enter another number: ")

    itemList.append(listStr)