def calc_num_ExoMol_trans(html_tags):
    """
    Calculate the number of .trans files in the line list

    Parameters
    ----------
    html_tags : TYPE
        DESCRIPTION.

    Returns
    -------
    counter : TYPE
        DESCRIPTION.

    """
    
    counter = 0
    for tag in html_tags:
        if tag.get('href').find('trans') != -1:
            counter += 1
    return counter