def FindSubstr(subseq, seq, expAt, wobble):
    """
    Here we search for model parts pre and post barcode within a sequence
    from reads.

    subseq (str) Subsequence within string we're looking for
    seq (str) Full sequence to search subseq within
    expAt (int) expected at location of subseq
    wobble (int) possible interval around expAt for which subseq can be found.
    """
    L = len(seq)
    K = len(subseq)
    for i in range(expAt - wobble, expAt + wobble + 1):
        if i >= 0 and i < L and seq[i:i+K] == subseq:
            return i

    return None