def find_overlap(s1, s2):
    """
    Find overlaps between two reads. Assume they are both in the same
    orientation (r1 is revcomp)
    Return 3 seuqnces: s1, overlap, s2
    Arguments:
    - `s1`: first sequence, this is mate 2 actually in our experiments
    - `s2`: last sequence, mate 1
    """
    for i in range(min(len(s1), len(s2)))[::-1]:
        if s1[-i:]==s2[:i]:
            return s1[:-i], s1[-i:], s2[i:]
    return s1, '', s2