import re


def lines_with_VTK_classes(src_file_name):
    """
    Return A string of line numbers to highlight that have vtk class mentions.
    :param src_file_name: The source file
    :return: A string of line numbers to highlight.
    """
    with open(src_file_name, 'r') as ifh:
        lines = ifh.readlines()
        line_number = 1
        reg = re.compile(r'(vtk[0-9a-zA-Z]*)')
        hl_lines = []
        for line in lines:
            if reg.search(line):
                hl_lines.append(str(line_number))
            line_number += 1
        hl_lines = ' '.join(hl_lines)
        hl_lines = 'hl_lines="' + hl_lines + '"\n'
    return hl_lines