code: def buy_limit_order(self, amount, price, base="btc", quote="usd", limit_price=None):
          
          data = {'amount': amount, 'price': price}
          if limit_price is not None:
              data['limit_price'] = limit_price
          url = self._construct_url("buy/", base, quote)
          return self._post(url, data=data, return_json=True, version=2)
docs: Order to buy amount of bitcoins for specified price.