@staticmethod
def _normalize_compare_config(diff):
    """Filter out strings that should not show up in the diff."""
    ignore_strings = ['Contextual Config Diffs', 'No changes were found',
        'file prompt quiet', 'ntp clock-period']
    new_list = []
    for line in diff.splitlines():
        for ignore in ignore_strings:
            if ignore in line:
                break
        else:
            new_list.append(line)
    return '\n'.join(new_list)
