How to use the asteval.astutils.Empty function in asteval

return OPERATORS[op.__class__]


class Empty:
    """Empty class."""

    def __init__(self):
        """TODO: docstring in public method."""
        pass

    def __nonzero__(self):
        """TODO: docstring in magic method."""
        return False


ReturnedNone = Empty()


class ExceptionHolder(object):
    """Basic exception handler."""

    def __init__(self, node, exc=None, msg='', expr=None, lineno=None):
        """TODO: docstring in public method."""
        self.node = node
        self.expr = expr
        self.msg = msg
        self.exc = exc
        self.lineno = lineno
        self.exc_info = exc_info()
        if self.exc is None and self.exc_info[0] is not None:
            self.exc = self.exc_info[0]
        if self.msg == '' and self.exc_info[1] is not None: