What is the minus 1 in line 3 actually doing in this loop? “max_index = len(words) - 1“.

Question

1. words = ["hello", "world", "spam", "eggs"]
2. counter = 0
3. max_index = len(words) - 1

4. while counter <= max_index:
5. word = words[counter]
6. print(word + "!")
7. counter = counter + 1

Answer 1

Words has 4 items in the list. A list uses a zero based index so the 1st item is at index 0 and in this case the last item is at index 3. len(words) will return a length of 4. The length of a list minus 1 will give you the integer for the last index in a list. In this case 3. This insures that you don't attempt to access an item via an index that is beyond the end of the list.