For loop prints strane values?

[ichabod801]

You are misunderstanding indexes. Think of the indexes as being between the items, rather than on the items:

Output:
lunch = ['Spam', 'spam', 'spam', 'eggs', 'spam']
        ^       ^       ^       ^       ^      ^
        |       |       |       |       |      |
        0       1       2       3       4      5
       -5      -4      -3      -2      -1     

If you just give one index, you get the item after it. But if you give two indexes, you get everything between them. So lunch[0:5] is five items, not six.