List number

Question

What's the number of each word?
For example:
words = ["a","b","c"]
print(words[0])
print(words[-1])
print(words[-2])

Why does it output
a
c
b

instead of
c
b
a

Does zero always stand for the first one?
And Why can

print(words[-1])
print(words[-2])
print(words[-3])

work but

print(words[1])
print(words[2])
print(words[3])

can't?

Answer 1

words[-1], words [-2], words [-3]
stand for the last, second_last and third_last elements of the list:

indexing always starts from 0:
thus,
print(words[3]) will not work since index 3 stands for the fourth element of the list, which is non-existent

Answer 2

Index 0 always stans for the first element. Index -1 is the last element, -2 for the second to last. -3 is ok in your case, meaning the third but last (actually, the first element in a list with 3 members). Index 3 is out of range in your example –the last element has index 2 (as well as -1).

Answer 3

Think at the list as circular: before the first element ( index -1 ) stand the last element ;)