def METHOD_NAME(self, node, reason=None):
    """Warn the user that a given chunk of code is not valid Python 3,
    but that it cannot be converted automatically.
    First argument is the top-level node for the code in question.
    Optional second argument is why it can't be converted.
    """
    lineno = node.get_lineno()
    for_output = node.clone()
    for_output.prefix = u""
    msg = "Line %d: could not convert: %s"
    self.log_message(msg % (lineno, for_output))
    if reason:
        self.log_message(reason)