def get_site_len_list(len_in):
    """
    Read in site lengths (one length per row from file len_in).
    Return list of lengths.

    """
    site_len_list = []

    with open(len_in) as f:
        for line in f:
            site_len = line.strip()
            site_len_list.append(int(site_len))
    f.closed
    assert site_len_list, "site_len_list empty (no lengths read in from %s)" %(len_in)
    return site_len_list