def check_once(self, func):
self.add_check(func, call_once=True)<EOL>return func<EOL>
r"""A decorator that adds a "call once" global check to the bot.

        Unlike regular global checks, this one is called only once
        per :meth:`.Command.invoke` call.

        Regular global checks are called whenever a command is called
        or :meth:`.Command.can_run` is called. This type of check
        bypasses that and ensures that it's called only once, even inside
        the default help command.

        .. note::

            This function can either be a regular function or a coroutine.

        Similar to a command :func:`.check`\, this takes a single parameter
        of type :class:`.Context` and can only raise exceptions inherited from
        :exc:`.CommandError`.

        Example
        ---------

        .. code-block:: python3

            @bot.check_once
            def whitelist(ctx):
                return ctx.message.author.id in my_whitelist