def _labels_input_string(inp_str):
    """ Read the labels out of a MESS input file
    """

    def _read_label(line, header):
        """ Get a labe from a line
        """
        lbl = None
        idx = 2 if header != 'Barrier' else 4
        line_lst = line.split()
        if len(line_lst) == idx and '!' not in line:
            lbl = line_lst[idx]
        return lbl

    lbls = ()
    for line in inp_str.splitlines():
        if 'Well ' in line:
            lbls += (_read_label(line, 'Well'),)
        elif 'Bimolecular ' in line:
            lbls += (_read_label(line, 'Bimolecular'),)
        elif 'Barrier ' in line:
            lbls += (_read_label(line, 'Barrier'),)

    return lbls