code: def book(self, name):
          
          self._validate_order_book(name)
          return OrderBook(name, self._rest_client, self._logger)
docs: Return an API wrapper for the given order book.
  
          :param name: Order book name (e.g. "btc_cad").
          :type name: str | unicode
          :return: Order book API wrapper.
          :rtype: quadriga.book.OrderBook
          :raise InvalidOrderBookError: If an invalid order book is given.
  
          **Example**:
  
          .. doctest::
  
              >>> from quadriga import QuadrigaClient
              >>>
              >>> client = QuadrigaClient()
              >>>
              >>> eth = client.book('eth_cad').get_ticker()  # doctest:+ELLIPSIS
              >>> btc = client.book('btc_cad').get_ticker()  # doctest:+ELLIPSIS