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

def get_ast_names(astnode):
    """Return symbol Names from an AST node."""
    finder = NameFinder()
    finder.generic_visit(astnode)
    return finder.names

def model(self, value):
        if callable(value):
            model = value()
        else:
            model = value
        self._model = model
        self.current_result = None
        self._current_params = model.make_params()

        # Use these to evaluate any Parameters that use expressions.
        self.asteval = Interpreter()
        self.namefinder = NameFinder()

        self._finalize_model(value)

        self.guess()