Is there any difference betwwen these two forms of for-loop?

Question

I have set of patterns

ATGCG GCATG CATGC AGGCA GGCAT

which I need to find the overlap between them. I'm using this function and it works correctly:

def get_overlap(patterns):
    n = len(patterns[0])-1
    return [(left,right) for left,right in product(patterns,patterns) if left != right and left.endswith(right[:n])]

My question is: why it doesn't loop through all the patterns when I am using the ordinary for loop form?

for left, right in product(patterns, patterns):
    if left != right and left.endswith(right[:n]):
        return [left, right]

it prints the last item only

score 3 · Accepted Answer · answered Dec 04 '14 at 10:32

The first solution basically says "return all (left, right) pairs that match the following criteria"

The second solution says "search for a pair, that matches the following criteria. As soon as one is found, return it". Therefore only one is returned. I haven't tested this, but I it should be the first one encountered, not the last one.

To fix it: instead of returning a pair which is found in the second solution, add it to an array of solutions, and return that array after the for loop.

Is there any difference betwwen these two forms of for-loop?

1 Answers1