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

def node_assign(self, node, val):
        """Assign a value (not the node.value object) to a node.

        This is used by on_assign, but also by for, list comprehension,
        etc.

        """
        if node.__class__ == ast.Name:
            if not valid_symbol_name(node.id) or node.id in self.readonly_symbols:
                errmsg = "invalid symbol name (reserved word?) %s" % node.id
                self.raise_exception(node, exc=NameError, msg=errmsg)
            self.symtable[node.id] = val
            if node.id in self.no_deepcopy:
                self.no_deepcopy.remove(node.id)

        elif node.__class__ == ast.Attribute:
            if node.ctx.__class__ == ast.Load:
                msg = "cannot assign to attribute %s" % node.attr
                self.raise_exception(node, exc=AttributeError, msg=msg)

            setattr(self.run(node.value), node.attr, val)

        elif node.__class__ == ast.Subscript:
            sym = self.run(node.value)
            xslice = self.run(node.slice)

def on_functiondef(self, node):
        """Define procedures."""
        # ('name', 'args', 'body', 'decorator_list')
        if node.decorator_list:
            raise Warning("decorated procedures not supported!")
        kwargs = []

        if not valid_symbol_name(node.name) or node.name in self.readonly_symbols:
            errmsg = "invalid function name (reserved word?) %s" % node.name
            self.raise_exception(node, exc=NameError, msg=errmsg)

        offset = len(node.args.args) - len(node.args.defaults)
        for idef, defnode in enumerate(node.args.defaults):
            defval = self.run(defnode)
            keyval = self.run(node.args.args[idef+offset])
            kwargs.append((keyval, defval))

        args = [tnode.arg for tnode in node.args.args[:offset]]
        doc = None
        nb0 = node.body[0]
        if isinstance(nb0, ast.Expr) and isinstance(nb0.value, ast.Str):
            doc = nb0.value.s

        varkws = node.args.kwarg