Python Loop Double Printing

You should zip instead of a nested loop to iterate both lists concurrently:

forwardOutright = [x+y for x, y in zip(spot, forwardSwap)]

As per the given code in your question, both of your loops are using a variable named as i.

for i in range(len(spot)):
    for i in range(len(forwardSwap)):

This should work

list(map(lambda i: sum(i), zip(spot, forwardSwap)))