Writing a function that alternates plus and minus signs between list indices

Question

In a homework set I\'m working on, I\'ve come across the following question, which I am having trouble answering in a Python-3 function:

\"Write a fun

Answer 1

Here is one way using operator module:

In [21]: from operator import pos, neg

In [23]: ops = (pos, neg)

In [24]: sum(ops[ind%2](value) for ind, value in enumerate(lst))
Out[24]: -2