Check if the given order book is valid.

        :param book: Order book name.
        :type book: str | unicode
        :raise InvalidOrderBookError: If an invalid order book is given.

def _validate_order_book(self, book):
        """Check if the given order book is valid.

        :param book: Order book name.
        :type book: str | unicode
        :raise InvalidOrderBookError: If an invalid order book is given.
        """
        if book not in self.order_books:
            raise InvalidOrderBookError(
                'Invalid order book \'{}\'. Choose from {}.'
                .format(book, tuple(self.order_books))
            )