Question

How would you approach comparing two lists and “looking back”?

I’m comparing the elements of two lists like this:

score = 0
for (x,y) in zip(seqA,seqB):

    if x == y:
        score = score +1

    if x !=y :
        score = score - 1

Now I would like score + 3 if the previous pair was a match, so basically I would have to “look back” one iteration.

Answer 1

Just save the result of the last match.

score = 0
prev  = 0

for (x,y) in zip(seqA,seqB):

    if x == y:
        if prev == 1:
            score = score +3
        else:
            score = score +1
        prev = 1

    if x !=y :
        score = score - 1
        prev = 0