Negative list index?
Question:
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?
Answers:
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.
List indexes of -x mean the xth item from the end of the list, so n[-1] means the last item in the list n. Any good Python tutorial should have told you this.
It’s an unusual convention that only a few other languages besides Python have adopted, but it is extraordinarily useful; in any other language you’ll spend a lot of time writing n[n.length-1] to access the last item of a list.
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?
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.
List indexes of -x mean the xth item from the end of the list, so n[-1] means the last item in the list n. Any good Python tutorial should have told you this.
It’s an unusual convention that only a few other languages besides Python have adopted, but it is extraordinarily useful; in any other language you’ll spend a lot of time writing n[n.length-1] to access the last item of a list.