def diff_lines(self, prev):
    lines = difflib.ndiff(prev.lines, self.lines)
    return [l.strip() for l in lines if (l.startswith('+') or l.startswith('-'))]
def diff_lines(self, prev):
    lines = difflib.ndiff(prev.lines, self.lines)
    return [l.strip() for l in lines if (l.startswith('+') or l.startswith('-'))]