<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fetch_list(cls, client, ids):
 """ fetch instruments by ids """

        results = []
        request_url = "https://api.robinhood.com/options/instruments/"

        for _ids in chunked_list(ids, 50):

            params = {"ids": ",".join(_ids)}
            data = client.get(request_url, params=params)
            partial_results = data["results"]

            while data["next"]:
                data = client.get(data["next"])
                partial_results.extend(data["results"])
            results.extend(partial_results)

        return results