PYTHON error index out of range

Question

There I was trying to create a script that did permutation, create a combination of the list items in a new list. Follow the python code:

itens = []
while True:
          adition = input('Coloque os itens: ')
          if adition == 'end':
                    break
          else:
                    itens.append(adition)
                    print(adition)
comb = []

for i in itens:
           contagem = 0
           while True:
                     comb.append(i + itens[contagem])
                     print(comb)
                     if contagem == len(itens):
                               break
                     else:
                               contagem = contagem + 1

But when I run the command and put the items in the list returns the following error:

Comb.append(i+items[count])

Indexerror: list index out of range

Answer 1

Elevate the condition if contagem == len(itens) to run before accessing itens[contagem]

while True:
    if contagem == len(itens):
        break
    else:
        comb.append(i + itens[contagem])
        print(comb)
        contagem = contagem + 1

The error happens in your code because you try to access the position contagem from your list before validating whether it is valid.

---

Suppose that itens own both items: a and b.

In the first iteration cont is equal to 0

He picks up a at position 0 and generates aa

In the second iteration cont is equal to 1

He picks up b at position 1 and generates ab

In the third iteration cont is equal to 2

He tries to pick up the item at position 2, which does not exist, and so the error.

---

A simpler way of writing this logic would be

while contagem < len(itens):
    comb.append(i + itens[contagem])
    print(comb)
    contagem = contagem + 1

Or use another loop for

for i in itens:
    for i2 in itens:
        comb.append(i + i2)
        print(comb)