python - Negative list index?

Possible Duplicate:
Explain slice notation

I'm trying to understand the following piece of code:

# node list
n = []
for i in xrange(1, numnodes + 1):
    tmp = session.newobject();
    n.append(tmp)
link(n[0], n[-1])

Specifically, I don't understand what the index -1 refers to. If the index 0 refers to the first element, then what does -1 refer to?

Answer

Negative numbers mean that you count from the right instead of the left. So, list[-1] refers to the last element, list[-2] is the second-last, and so on.