def return_start_end(seq):
    """ Returns the start and end indices of amino acids  """    
    start = next(idx for (idx,s) in enumerate(seq) if s != '-')
    try:
        end = start -1 + next(idx for (idx,s) in enumerate(seq[start:]) if s == '-')
    except StopIteration:
        end = len(seq) - 1

    return start,end