creating sum of odd indexes python

Question

I\'m trying to create a function equal to the sum of every other digit in a list. For example, if the list is [0,1,2,3,4,5], the function should equal 5+3+1. How could I do

Answer 1

>>> arr = [0,1,2,3,4,5]
>>> sum([x for idx, x in enumerate(arr) if idx%2 != 0])
9

This is just a list comprehension that only includes elements in arr that have an odd index.

To illustrate in a traditional for loop:

>>> my_sum = 0
>>> for idx, x in enumerate(arr):
...     if idx % 2 != 0:
...         my_sum += x
...         print("%d was odd, so %d was added. Current sum is %d" % (idx, x, my_sum))
...     else:
...         print("%d was even, so %d was not added. Current sum is %d" % (idx, x, my_sum))
... 
0 was even, so 0 was not added. Current sum is 0
1 was odd, so 1 was added. Current sum is 1
2 was even, so 2 was not added. Current sum is 1
3 was odd, so 3 was added. Current sum is 4
4 was even, so 4 was not added. Current sum is 4
5 was odd, so 5 was added. Current sum is 9