<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def stream(self, to=values.unset, from_=values.unset, parent_call_sid=values.unset, status=values.unset, start_time_before=values.unset, start_time=values.unset, start_time_after=values.unset, end_time_before=values.unset, end_time=values.unset, end_time_after=values.unset, limit=None, page_size=None):
 """ Streams CallInstance records from the API as a generator stream. This operation lazily loads records as efficiently as possible until the limit is reached. The results are returned as a generator, so this operation is memory efficient. :param unicode to: Phone number or Client identifier of calls to include :param unicode from_: Phone number or Client identifier to filter `from` on :param unicode parent_call_sid: Parent call SID to filter on :param CallInstance.Status status: The status of the resources to read :param datetime start_time_before: Only include calls that started on or after this date :param datetime start_time: Only include calls that started on or after this date :param datetime start_time_after: Only include calls that started on or after this date :param datetime end_time_before: Only include usage that occurred on or before this date :param datetime end_time: Only include usage that occurred on or before this date :param datetime end_time_after: Only include usage that occurred on or before this date :param int limit: Upper limit for the number of records to return. stream() guarantees to never return more than limit. Default is no limit :param int page_size: Number of records to fetch per request, when not set will use the default value of 50 records. If no page_size is defined but a limit is defined, stream() will attempt to read the limit with the most efficient page size, i.e. min(limit, 1000) :returns: Generator that will yield up to limit results :rtype: list[twilio.rest.api.v2010.account.call.CallInstance] """

        limits = self._version.read_limits(limit, page_size)

        page = self.page(
            to=to,
            from_=from_,
            parent_call_sid=parent_call_sid,
            status=status,
            start_time_before=start_time_before,
            start_time=start_time,
            start_time_after=start_time_after,
            end_time_before=end_time_before,
            end_time=end_time,
            end_time_after=end_time_after,
            page_size=limits['page_size'],
        )

        return self._version.stream(page, limits['limit'], limits['page_limit'])