code: def order_book(self, symbol, parameters=None):
          
          data = self._get(self.url_for(PATH_ORDERBOOK, path_arg=symbol, parameters=parameters))
  
          for type_ in data.keys():
              for list_ in data[type_]:
                  for key, value in list_.items():
                      list_[key] = float(value)
  
          return data
docs: curl "https://api.bitfinex.com/v1/book/btcusd"
  
          {"bids":[{"price":"561.1101","amount":"0.985","timestamp":"1395557729.0"}],"asks":[{"price":"562.9999","amount":"0.985","timestamp":"1395557711.0"}]}
  
          The 'bids' and 'asks' arrays will have multiple bid and ask dicts.
  
          Optional parameters
  
          limit_bids (int): Optional. Limit the number of bids returned. May be 0 in which case the array of bids is empty. Default is 50.
          limit_asks (int): Optional. Limit the number of asks returned. May be 0 in which case the array of asks is empty. Default is 50.
  
          eg.
          curl "https://api.bitfinex.com/v1/book/btcusd?limit_bids=1&limit_asks=0"
          {"bids":[{"price":"561.1101","amount":"0.985","timestamp":"1395557729.0"}],"asks":[]}