How do Negative List Indexes Work in Python?

Understanding Negative List Indexes

Negative numbers in Python lists are used for counting elements from the end rather than the beginning. In the provided code:

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

The line n[-1] accesses the last element of the n list. Similarly, n[-2] would refer to the second last element. This is because Python indexes lists from zero, so the first element has an index of 0, the second element has an index of 1, and so on.

By using negative indexes, you can access elements from the right end of the list without knowing its exact size. This is particularly useful when working with dynamic lists or when the number of elements is not known in advance.

For example, to print the last three elements of a list my_list, you can use:

for item in my_list[-3:]:
    print(item)

This approach is more flexible and efficient compared to using positive indexes and calculating the length of the list.

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